#internals-and-peps | Python | Page 70

feral bane Sep 4, 2020, 12:05 AM

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i guess you could make it so the keyword is only allowed in funtions

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might be slightl confusing

grave jolt Sep 4, 2020, 12:06 AM

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and if it's inside a function, it's hopefully easy to see than a variable is not mutated 🙂

gleaming rover Sep 4, 2020, 12:07 AM

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and if it's inside a function, it's hopefully easy to see than a variable is not mutated 🙂
@grave jolt yeah, that's what I was thinking

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because IIRC Final doesn't work for local variables?

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and it would be nice to have something that a 3rd-party checker could pick up

feral bane Sep 4, 2020, 12:14 AM

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inside a function could allow more optimizations too

gleaming rover Sep 4, 2020, 12:14 AM

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inside a function could allow more optimizations too
@feral bane it could, but it would also be significantly more work for the core team, I guess

raven ridge Sep 4, 2020, 1:03 AM

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I mean like:

const x = 1
x = 2  # SyntaxError

@gleaming rover how's it interact with nonlocal? With globals()? With exec?

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With rebinding from another module? What if there was:
a.py:

const x = 0

b.py:

import a
a.x = 10

feral bane Sep 4, 2020, 1:42 AM

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nonlocal shouldn't be a problem

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lookup for nonlocal isn't dynamic, it knows when it's compiled what function the variable is from

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i do think it's untenable to try to do this for scopes that aren't functions

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though you could conceivably make a descriptor that does it for instance variables

feral bane Sep 4, 2020, 2:00 AM

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class InitOnlyVar:
    def __init__(self):
        self.default = default
    def __get__(self, obj, objtype=None):
        return obj.__dict__[self.name]
    def __set__(self, obj, val):
        if self.name in obj.__dict__:
            raise AttributeError("readonly attribute")
        obj.__dict__[self.name] = val
    def __set_name__(self):
        self.name = value

class InitOnlySlotVar:
    def __init__(self, name, descriptor):
        self.descriptor = descriptor
        self.name = name
    def __get__(self, obj, objtype=None):
        return self.descriptor.__get__(self, obj, objtype)
    def __set__(self, obj, val):
        try:
            self.descriptor.__get__(self, obj)
        except AttributeError: #good
            self.descriptor.__set__(obj, val)
        else:
            raise AttributeError("readonly attribute")

def setup_initonly_slots(cls):
    # called after class definition
    slots = cls.__initonly_slots__
    if isinstance(slots, str): slots = (slots,)
    for name in slots:
        desc = InitOnlySlotVar(name, getattr(cls, name))
        setattr(cls, name, desc)

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to use the regular one just use varname = InitOnlyVar(), and it creates a descriptor that can only be assigned once,

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to use the slot one, define __slots__ as normal, __initonly_slots__ as the ones you want to have this behavior, and then call setup_initonly_slots(Class) after the class is defined

gleaming rover Sep 4, 2020, 2:02 AM

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@gleaming rover how's it interact with nonlocal? With globals()? With exec?
@raven ridge you mean at runtime?

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honestly I forgot about Final

teal yacht Sep 4, 2020, 2:04 AM

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with how breakable python is, having static analysis tools send a nice f-u message to people abusing its """"features"""", or straight up pretending they don't exist is the best we can do

pseudo cradle Sep 4, 2020, 2:22 AM

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Sometimes I wonder what dynamic typing really brings to the language

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I can't really think of anything

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Other than saving you time from typing things out

gleaming rover Sep 4, 2020, 2:23 AM

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Other than saving you time from typing things out
@pseudo cradle type inference helps with that

teal yacht Sep 4, 2020, 2:23 AM

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because there isn't anything, programs generally aren't even designed in a way that takes advantage of dynamic typing

feral cedar Sep 4, 2020, 2:23 AM

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it looks nice

gleaming rover Sep 4, 2020, 2:23 AM

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I'd say the main advantage of dynamic typing is letting you write programs that "almost work" quickly

teal yacht Sep 4, 2020, 2:23 AM

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i guess if people are fine with that shrug

pseudo cradle Sep 4, 2020, 2:23 AM

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It's also the main disadvantage, tbh

gleaming rover Sep 4, 2020, 2:24 AM

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i guess if people are fine with that :shrug:
@teal yacht throwaway scripts + small programs I guess

teal yacht Sep 4, 2020, 2:24 AM

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i think "almost working" is worse than "never working" in a crushing majority of case tho

pseudo cradle Sep 4, 2020, 2:24 AM

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Like, even if you just really really need dynamic typing that's what unions are for?

gleaming rover Sep 4, 2020, 2:24 AM

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Like, even if you just really really need dynamic typing that's what unions are for?
@pseudo cradle that's not what unions are for IMO

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you mean like sum types?

pseudo cradle Sep 4, 2020, 2:25 AM

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Like, if you're trying to declare the return type of a function and you don't know if it's going to be a list or a bool

gleaming rover Sep 4, 2020, 2:25 AM

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uh...

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that seems somehow orthogonal

pseudo cradle Sep 4, 2020, 2:25 AM

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(Was an example I saw on SO)

teal yacht Sep 4, 2020, 2:25 AM

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i just wish global type inference was standard and we'd just never write types anymore

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i swear python code has more types written than f#

gleaming rover Sep 4, 2020, 2:26 AM

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i just wish global type inference was standard and we'd just never write types anymore
@teal yacht isn't it undecidable in the general case

teal yacht Sep 4, 2020, 2:26 AM

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depends on the type system, but yeah in common oop-like type systems, it's not decidable

raven ridge Sep 4, 2020, 2:27 AM

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@raven ridge you mean at runtime?
@gleaming rover yeah.

gleaming rover Sep 4, 2020, 2:28 AM

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@gleaming rover yeah.
@raven ridge I was thinking a compile-time check, and then, yes, I remembered Final

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although on that topic the equivalent of descriptors for modules would be nice too

raven ridge Sep 4, 2020, 2:33 AM

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my point is that a compile time check isn't sufficient - Python is such a dynamic language that there's no way a compile-time check will do the trick.

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it can't possibly prevent something like:

def func(stmt):
    const x = 0
    eval(stmt)
    print(x)
func("x = 5")```

gleaming rover Sep 4, 2020, 2:34 AM

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no

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I was envisioning something like type hints

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i.e. no runtime enforcement by design

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which is why I mentioned Final

raven ridge Sep 4, 2020, 2:34 AM

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ah. 🤷

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I mean, it'd give linting one extra mistake it could catch. But if we're talking about language changes that would make linting more effective, I don't think that's the most effective one...

gleaming rover Sep 4, 2020, 2:42 AM

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I mean, it'd give linting one extra mistake it could catch. But if we're talking about language changes that would make linting more effective, I don't think that's the most effective one...
@raven ridge probably not? but it's something that's personally relevant to me because I more or less never reassign

raven ridge Sep 4, 2020, 2:57 AM

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some of the suggestions above would basically just be a different language. "Python, except with static typing", even with perfect type inference, would just be an entirely different language than Python.

gleaming rover Sep 4, 2020, 2:58 AM

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some of the suggestions above would basically just be a different language. "Python, except with static typing", even with perfect type inference, would just be an entirely different language than Python.
@raven ridge did anyone suggest Python but statically typed?

raven ridge Sep 4, 2020, 2:58 AM

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Sometimes I wonder what dynamic typing really brings to the language
@pseudo cradle I mean, pretty much 😄

gleaming rover Sep 4, 2020, 2:59 AM

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fair enough

teal yacht Sep 4, 2020, 2:59 AM

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mypy with --disallow-untyped-functions would be statically typed python

pseudo cradle Sep 4, 2020, 2:59 AM

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I'm going through and type hinting everything anyway

raven ridge Sep 4, 2020, 2:59 AM

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mypy is... not good.

pseudo cradle Sep 4, 2020, 3:00 AM

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Or at least making a half-hearted attempt to and giving up

raven ridge Sep 4, 2020, 3:00 AM

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I literally can't use mypy in a medium sized project without finding a bug, or limitation, that makes me need to go through ridiculous contrivances to work around it.

gleaming rover Sep 4, 2020, 3:00 AM

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I literally can't use mypy in a medium sized project without finding a bug, or limitation, that makes me need to go through ridiculous contrivances to work around it.
@raven ridge indeed.

teal yacht Sep 4, 2020, 3:00 AM

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i wouldn't call it good either, but it's orders of magnitude better than nothing imo

gleaming rover Sep 4, 2020, 3:00 AM

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also having to use untyped libraries is just 😦

raven ridge Sep 4, 2020, 3:00 AM

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and there are common Python idioms that mypy just throws up it's hands about.

teal yacht Sep 4, 2020, 3:01 AM

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honestly i find it unusable atm because nobody uses it, it's a terrible vicious circle

raven ridge Sep 4, 2020, 3:01 AM

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_NOT_SET = object()
def some_func(param=_NOT_SET):
   ...

Try typing this. Whoops.

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I actually do use mypy.

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my team had a vote, I lost 😄

teal yacht Sep 4, 2020, 3:02 AM

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i don't think every python code is worth existing tbh

raven ridge Sep 4, 2020, 3:02 AM

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I don't like it, and find it ridiculously frustrating. More than once I've had to rewrite code to get it into a different form that mypy could adequately describe, heh

teal yacht Sep 4, 2020, 3:02 AM

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type systems by their very definition make some programs invalid

raven ridge Sep 4, 2020, 3:03 AM

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i don't think every python code is worth existing tbh
@teal yacht fair enough, but that was a common Python idiom for a very long time.

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there is tons of existing code, part of public interfaces, that cannot be described by mypy. That's not ideal.

safe hedge Sep 4, 2020, 3:03 AM

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I just find typehints get unwieldy very fast when dealing with highly variable data

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Unless you just say fuck it and pass Any half the time

teal yacht Sep 4, 2020, 3:04 AM

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the goal is to find a way to express logic through the type system, minimizing the amount of buggy program that gets validated, while maximizing the amount of program that does get validated

safe hedge Sep 4, 2020, 3:04 AM

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Because constructing the actual type hint for the allowed types gets really long and convoluted

teal yacht Sep 4, 2020, 3:04 AM

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look up protocols

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and learn about the standard abstract classes

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these are so underused it makes me sad

raven ridge Sep 4, 2020, 3:05 AM

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the goal is to find a way to express logic through the type system, minimizing the amount of buggy program that gets validated, while maximizing the amount of program that does get validated
@teal yacht if you're writing brand new code, perhaps. But when you're trying to add annotations to existing code (that was idiomatic before mypy existed!) it's nothing but disappointment.

teal yacht Sep 4, 2020, 3:05 AM

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especially in a language like python, structural subtyping is a blessing

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it's just so uncommon in programming in general that it's hard to make it take off

raven ridge Sep 4, 2020, 3:05 AM

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the structural subtyping stuff in mypy actually is pretty cool. 🙂

safe hedge Sep 4, 2020, 3:07 AM

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Like this is grim imo: Dict[Union[str, int], Dict[Union[str, int], Union[str, int, None, Dict[Union[str, int], str]]]

raven ridge Sep 4, 2020, 3:09 AM

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Sphinx now reads type hints and uses it to infer types for parameters. It almost works.

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I have an API that I haven't yet figured out any meaningful way to type, actually. I've just thrown up my hands and given up on it.

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I've got a DB-API 2.0 compliant database API that allows the user to set a row_factory property on a Connection to control the type of result rows. So you can do conn.row_factory = namedtuple_row_factory to get rows as namedtuple instances, or conn.row_factory = dict_row_factory to get rows as keys, etc.

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so the method that fetches a row from the database returns - well, any type of object at all. It's a type of object that the user configured in advance, but there's no way to describe that to mypy

safe hedge Sep 4, 2020, 3:13 AM

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That's just Any no?

raven ridge Sep 4, 2020, 3:13 AM

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I mean, maybe, but then the user is forced to cast to a type they've already configured.

safe hedge Sep 4, 2020, 3:13 AM

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I mean really what you've got there is a limitation of static-type checking when you have a dynamic type

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If you are allowing the user to dynamically define the return type how can you possibly expect mypy to check that

raven ridge Sep 4, 2020, 3:15 AM

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conn.row_factory = dict_row_factory
for row in conn:
    print(row.keys())

Typing that as Any won't make mypy happy. Typing it as Dict is a lie in the general case. The user needs to do something ridiculous like:

conn.row_factory = dict_row_factory
for row in cast(Dict[str, Any], conn.execute(statement)):
    ...

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If you are allowing the user to dynamically define the return type how can you possibly expect mypy to check that
@safe hedge I mean, I agree, but I've got users that are all like "why doesn't this library have type hints blah blah blah"

gleaming rover Sep 4, 2020, 3:16 AM

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I mean really what you've got there is a limitation of static-type checking when you have a dynamic type
@safe hedge I'm pretty sure there's a way to type this in a sufficiently powerful static type system

raven ridge Sep 4, 2020, 3:16 AM

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and the answer is that, given the constraints of mypy, it cannot.

gleaming rover Sep 4, 2020, 3:16 AM

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because each factory knows its own type

safe hedge Sep 4, 2020, 3:17 AM

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But isn't the user providing the factory?

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Not just picking from a few available ones?

gleaming rover Sep 4, 2020, 3:17 AM

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as long as the factory is typed, it shouldn't matter

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like I'm not saying that mypy can do it

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but the equivalent pattern in a statically typed language should be doable

raven ridge Sep 4, 2020, 3:18 AM

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Not just picking from a few available ones?
@safe hedge technically, yes, though the library provides several, and in practice I've never seen anyone provide one that didn't come from the library.

safe hedge Sep 4, 2020, 3:18 AM

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How much of statically typed language do you want to incorporate before you just say fuck it and make python fully statically typed

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At some point you accept the trade-offs no?

raven ridge Sep 4, 2020, 3:19 AM

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I mean, I don't have a problem with dynamic typing. I find mypy annoying 🙂

safe hedge Sep 4, 2020, 3:19 AM

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I use typehints in my own code but mainly so I remember how I intended to use the functions tbh

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I don't even use a static type checker

gleaming rover Sep 4, 2020, 3:20 AM

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I don't even use a static type checker
@safe hedge do PyCharm's checks count

safe hedge Sep 4, 2020, 3:20 AM

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Well I use an editor not an ide..

raven ridge Sep 4, 2020, 3:20 AM

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I generally don't write application code, I generally write library code. So, users ask for type hints because they want to type their applications, and - well, sometimes I can provide them,, I guess.

safe hedge Sep 4, 2020, 3:20 AM

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I guess that's fair

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But tbh I think good documentation is fine

raven ridge Sep 4, 2020, 3:21 AM

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not when they want to mypy --strict their code.

safe hedge Sep 4, 2020, 3:21 AM

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Yeah but that's on them

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Sometimes I'm so glad the majority of code I write I am also the user

raven ridge Sep 4, 2020, 3:24 AM

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this is actually open sourced code I'm complaining about - it's https://bloomberg.github.io/python-comdb2/dbapi2.html#comdb2.dbapi2.Cursor.fetchone

feral cedar Sep 4, 2020, 3:26 AM

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huh

safe hedge Sep 4, 2020, 3:26 AM

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@raven ridge Hmm, that's basically like DictCursor from pymysql right?

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Does that have typehints?

raven ridge Sep 4, 2020, 3:26 AM

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don't know pymysql, but that sounds like it's probably similar.

low lagoon Sep 4, 2020, 3:26 AM

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@fast hamlet this isn't relevant to anything here.

safe hedge Sep 4, 2020, 3:27 AM

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psycopg2 has one too

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Hmm psycopg2 doesn't have typehints

raven ridge Sep 4, 2020, 3:28 AM

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yep. The idea of making the row type configurable is pretty common across DB-API interfaces.

safe hedge Sep 4, 2020, 3:29 AM

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Unless you're pyodbc which just leaves it up to you

raven ridge Sep 4, 2020, 3:29 AM

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and I expect none of them have figured out any way to type this, because as far as I've been able to tell mypy is insufficiently expressive to handle it. 🙂

safe hedge Sep 4, 2020, 3:29 AM

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Although I presume that in reality all implementations are just wrappers around the standard return type of a list

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Like the pyodbc recommended method to get dicts is:

raven ridge Sep 4, 2020, 3:30 AM

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in some sense - the database returns one particular type of thing, at the level of the wire protocol, and then the DB-API interface is responsible for massaging that into Python types for the user to consume.

safe hedge Sep 4, 2020, 3:30 AM

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columns = [c[0] for c in cursor.description]
res = [dict(zip(columns, r)) for r in cursor]

raven ridge Sep 4, 2020, 3:31 AM

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https://bloomberg.github.io/python-comdb2/_modules/comdb2/factories.html#dict_row_factory - yep, basically.

safe hedge Sep 4, 2020, 3:32 AM

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Also it's not strictly part of the DBAPI spec: https://www.python.org/dev/peps/pep-0249/#frequently-asked-questions

Python.org

PEP 249 -- Python Database API Specification v2.0

The official home of the Python Programming Language

raven ridge Sep 4, 2020, 3:33 AM

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yep, very true. The spec only requires a ~~tuple~~sequence of column values.

safe hedge Sep 4, 2020, 3:34 AM

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I think psycopg2 is my favourite python db api

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I'm always frustrated using others that don't seem as well featured

raven ridge Sep 4, 2020, 3:38 AM

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I haven't used it. Any particular extensions that stand out?

safe hedge Sep 4, 2020, 3:41 AM

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psycopg2.sql is really useful for constructing arbitrary statements with escaped values

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Effectively allows you to safely parameterise table names for example

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I think it handles bulk inserts reasonably well too

radiant fulcrum Sep 4, 2020, 6:59 AM

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It doesn't do much to any filtering of formatting

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It only does very very basic escapes for table names because at the end of the day it's still string formatting

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Not to mention the confusing margin it adds when trying to tell people to not format queries like that as they go “but psycopg2 formats it like this"

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As for bulk inserts than that's a meme, with executemany being slower than just a for loop of executions which is pithink

paper echo Sep 4, 2020, 10:15 AM

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the emphasis on portability doesn't make much sense to me, SQL portability is kind of a joke anyway. not to mention that DBAPI implementations are also different that, even if the queries were the same, you would still often have to rewrite code if for some reason you switched databases in your application

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The row factory approach is pretty reasonable though

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Not hard to type annotate either now that we have protocols. But obviously you can't annotate the result from a dynamic query that's generated at runtime

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How do other typed languages handle that?

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I know "how does it work in Haskell" is a meme here but how does "arbitrarily typed IO" work in haskell?

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JSON, SQL, etc. which can return data of somewhat arbitrary types

flat gazelle Sep 4, 2020, 10:24 AM

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you just expect a certain inferred type and error/return Nothing if it does not fit

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haskell read works like that

hs>(read "4.0"):: Int
*** Exception: Prelude.read: no parse
hs>(read "4.0"):: Float
4.0

paper echo Sep 4, 2020, 10:35 AM

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I see

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So, something like that isn't really possible with static type checking

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Right?

flat gazelle Sep 4, 2020, 10:38 AM

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Elm has a slightly different system, where you essentially describe what structure you expect and it either fits and you get Some t, and Nothing otherwise. This pretty much allows you to do everything dynamic typing can. In haskell, you can afaik use optics for similar results.

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if you mean statically typed SQL queries, there is postgres-typed, which can check whether all the types match based on schema, but IDK if that is what you mean

paper echo Sep 4, 2020, 10:40 AM

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row: Tuple[int, float, float] = cursor.fetchone()

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There's basically no way to check this

flat gazelle Sep 4, 2020, 10:41 AM

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SQL is not turing complete, so it should be possible in at least some cases

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postgres-typed can for queries known at compile time

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once you get to dependent typing though, it gets somewhat messier

paper echo Sep 4, 2020, 10:42 AM

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Right, but in general you need to annotate the results of a query not for checking the results of the query but for making sure that the rest of the program knows what results you expect

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Whereas in one of these typed languages the types you expect from the query actually determine runtime behavior

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So even in Haskell you can't really check the types of an expression like that until runtime

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(Unless you parse the SQL code itself)

flat gazelle Sep 4, 2020, 10:44 AM

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ye, haskell cannot leave typechecking until runtime, as there is no runtime representation of types

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so you have to describe your schema somewhere

deft pagoda Sep 4, 2020, 1:36 PM

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what's happening here:

In [4]: def test(cls):
   ...:     def something(cls):
   ...:         print(dir(cls))
   ...:     cls.__init_subclass__ = something
   ...:     return cls
   ...:

In [5]: @test
   ...: class Test: ...

In [6]: class Test2(Test): ...
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-14348d06b900> in <module>
----> 1 class Test2(Test): ...

TypeError: something() missing 1 required positional argument: 'cls'

I can't figure out why __init_subclass__ isn't being passed any arguments

junior moat Sep 4, 2020, 1:39 PM

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because something is a function, you need to call the protocol with __get__ to bind cls

peak spoke Sep 4, 2020, 1:39 PM

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You need to bind it to the class object

deft pagoda Sep 4, 2020, 1:39 PM

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i tried __get__(None, cls)

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but had the same error

peak spoke Sep 4, 2020, 1:39 PM

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cls.__init_subclass__ = types.MethodType(something, cls) ought to work

junior moat Sep 4, 2020, 1:41 PM

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I did not know MethodType, I personnaly use something like:
cls.__init_subclass__ = something.__get__(cls, cls.__class__)

MethodType seems way cleaner 🙂

deft pagoda Sep 4, 2020, 1:42 PM

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both of these work

junior moat Sep 4, 2020, 1:47 PM

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pick the one you prefer then 🙂

deft pagoda Sep 4, 2020, 2:19 PM

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or not...:

In [28]: def test_deco(cls):
    ...:     def __init_subclass__(cls):
    ...:         print(cls)
    ...: 
    ...:     cls.__init_subclass__ = __init_subclass__.__get__(cls, cls.__class__)
    ...:     return cls
    ...: 
    ...: @test_deco
    ...: class Test:
    ...:     ...
    ...: 
    ...: class Test2(Test):
    ...:     ...
    ...: 
    ...: class Test3(Test2):
    ...:     ...
    ...:
<class '__main__.Test'>
<class '__main__.Test'>

__init_subclass__ isn't getting the correct argument passed in

junior moat Sep 4, 2020, 2:20 PM

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well, you bind __init_subclass within the test_deco you did at the begining

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it needs to be bound again with Test2 and Test3

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I don't think decorator are suited for what you do

deft pagoda Sep 4, 2020, 2:22 PM

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I've wrapped it with classmethod decorator:

def test_deco(cls):
    def __init_subclass__(cls):
        print(cls)

    cls.__init_subclass__ = classmethod(__init_subclass__)
    return cls

@test_deco
class Test:
    ...

class Test2(Test):
    ...

class Test3(Test2):
    ...

#

this works

junior moat Sep 4, 2020, 2:22 PM

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ho nice

deft pagoda Sep 4, 2020, 2:23 PM

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i'm not sure what magic it's doing, but i'll dig into it later

junior moat Sep 4, 2020, 2:23 PM

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I was going to suggest using a metaclass if you needed to add a function to the most derived impl of an inheritance

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@deft pagoda https://docs.python.org/3/howto/descriptor.html#static-methods-and-class-methods

deft pagoda Sep 4, 2020, 2:25 PM

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well, i have a metaclass solution to this hacky thing I'm doing

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but the decorator solution is simpler

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if I can get the methods to bind correctly

junior moat Sep 4, 2020, 2:25 PM

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this is hwo it is implemented, I've not thought of using the descriptor this way

deft pagoda Sep 4, 2020, 2:26 PM

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class ClassMethod(object):
    "Emulate PyClassMethod_Type() in Objects/funcobject.c"

    def __init__(self, f):
        self.f = f

    def __get__(self, obj, klass=None):
        if klass is None:
            klass = type(obj)
        def newfunc(*args):
            return self.f(klass, *args)
        return newfunc

they give this as the descriptor of classmethod

junior moat Sep 4, 2020, 2:28 PM

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yep

deft pagoda Sep 4, 2020, 2:29 PM

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here's the thing:

from inspect import signature

def parse_signature(signature):
    return str(signature)[1:-1].split(', ', 1)[1]

def additive_init(cls):
    def __init_subclass__(cls):
        def add_parent_init(init):
            self_args = parse_signature(signature(init))
            parent_args = parse_signature(signature(cls.__base__.__init__))

            globals_ = {'init': init, 'cls':cls}
            locals_ = {}
            wrapper = f"""
            def wrapper(self, {parent_args}, {self_args}):
                super(cls, self).__init__({parent_args})
                init(self, {self_args})
            """
            exec(dedent(wrapper), globals_, locals_)

            return locals_['wrapper']

        cls.__init__ = add_parent_init(cls.__init__)

    cls.__init_subclass__ = classmethod(__init_subclass__)
    return cls

@additive_init
class Person:
    def __init__(self, name): self.name = name

class Cyborg(Person):
    def __init__(self, version): self.version = version

class Android(Cyborg):
    def __init__(self, model): self.model = model

print(signature(Android))  # (name, version, model)

Just a way to add inits from subclasses so you don't have to keep re-typing it all

junior moat Sep 4, 2020, 2:30 PM

#

well, i have a metaclass solution to this hacky thing I'm doing

When you said hacky, I was actually far from the reality of what you were trying to achive 🙂

#

when you end up doing exec, IMO you're the level above hacky 😉

deft pagoda Sep 4, 2020, 2:31 PM

#

I think at some level of meta-programming exec is very useful and nearly necessary

junior moat Sep 4, 2020, 2:31 PM

#

(TBH I don't have better to offer so not saying that you should NOT do it)

deft pagoda Sep 4, 2020, 2:31 PM

#

dataclasses use exec as well -- most code generators will

junior moat Sep 4, 2020, 2:32 PM

#

actually for parameter forwarding I prefer the django approach: they define only named args, and forward **kw to parent

#

the base class itself might not take **kw, so you get errors if some args are not known

peak spoke Sep 4, 2020, 2:58 PM

#

namedtuples are the ones I know about using exec; when I had a problem with them the code was quite confusing to navigate while looking for the cause

faint wind Sep 4, 2020, 4:23 PM

#

anyone know any java disord server i can join?

swift imp Sep 4, 2020, 4:25 PM

#

Does anyone know how costly it is to add new fields to a numpy.struct_array?

paper echo Sep 4, 2020, 6:10 PM

#

@deft pagoda attrs doesnt afaik

#

i dont know why dataclasses should use exec tbh

narrow meadow Sep 4, 2020, 6:17 PM

#

здрасте

flat gazelle Sep 4, 2020, 6:51 PM

#

import random
def random_key(w):
    a ,= random.choices(*zip(*w.items()))
    return a
```should about do it

teal yacht Sep 4, 2020, 6:53 PM

#

forgot to unpack w.items()

flat gazelle Sep 4, 2020, 6:53 PM

#

oops

#

In [49]: Counter(random_key(w) for _ in range(1000))
Out[49]: Counter({'B': 761, 'A': 239})

In [50]: w
Out[50]: {'A': 1, 'B': 3}
```with that it seems to work

lone wagon Sep 4, 2020, 8:34 PM

#

How does machine learning work

radiant fulcrum Sep 4, 2020, 8:40 PM

#

@lone wagon better to ask that in #data-science-and-ml

lone wagon Sep 4, 2020, 8:40 PM

#

k

deft pagoda Sep 4, 2020, 10:46 PM

#

@paper echo theres one:
https://github.com/python-attrs/attrs/blob/bfd7bb49b467e7ab586deb475c23974a91df4dab/src/attr/_make.py#L274

paper echo Sep 4, 2020, 10:47 PM

#

ah interesting

#

that isnt exec'ing the class itself though

#

its some auxiliary thing

deft pagoda Sep 4, 2020, 10:49 PM

#

looks like a class def to me:

attr_class_template = [
        "class {}(tuple):".format(attr_class_name),
        "    __slots__ = ()",
    ]

worldly venture Sep 4, 2020, 11:38 PM

#

!unsilence

fallen slateBOT Sep 4, 2020, 11:38 PM

#

✅ unsilenced current channel.

peak spoke Sep 4, 2020, 11:39 PM

#

Is there any reason to use eval(compile(...)) over a direct exec? (from snippet linked above)

safe hedge Sep 5, 2020, 12:01 AM

#

As for bulk inserts than that's a meme, with executemany being slower than just a for loop of executions which is
@radiant fulcrum Use the correct function then: execute_values. And the point is that even that basic SQL formatting is more than other libs seem to offer

ivory warren Sep 5, 2020, 12:04 AM

#

Hey,please help me in #help-kiwi .

deft pagoda Sep 5, 2020, 12:05 AM

#

@ivory warren don't post in multiple channels for the same question, and this is not a help channel

magic turret Sep 5, 2020, 7:52 AM

#

is it legal to crawl emails

#

I need b2c France mails.

undone hare Sep 5, 2020, 11:42 AM

#

3.5.10 hype baby!

#

Yay!

#

Ya... y..

brave badger Sep 5, 2020, 11:58 AM

#

Yay 🥳

teal stone Sep 5, 2020, 11:59 AM

#

What does it mean **kwargs?

magic python Sep 5, 2020, 12:12 PM

#

@teal stone post in #python-discussion , this is the wrong channel

deft pagoda Sep 5, 2020, 12:13 PM

#

kwargs is short for keyword arguments

red solar Sep 5, 2020, 1:47 PM

#

Has anyone been following the infinity constant proposal and can bullet point it for me? The thread won’t load for me for some reason 😦

undone hare Sep 5, 2020, 1:50 PM

#

I haven't looked at the thread, but what about float('inf')?

red solar Sep 5, 2020, 1:51 PM

#

I think they want a more standalone constant

deft pagoda Sep 5, 2020, 2:13 PM

#

math has them too

#

but I haven't seen any other proposals

#

that is, math.inf

undone hare Sep 5, 2020, 2:14 PM

#

To be honest, even defining INFINITY = float('inf') isn't too bad

deft pagoda Sep 5, 2020, 2:14 PM

#

i use float('inf') a lot by itself

#

and -float('inf')

sacred tinsel Sep 5, 2020, 5:27 PM

#

@red solar The proposal makes the following points:

It is also a fundamental constant (similar to True, False, and None), and should be representable as such in the language

Requiring a cast from float to string is messy, and also obviously less efficient (but this performance difference is likely insignificant)

Further, having a function call for something that should be a constant is a code-smell; in general str -> float conversion may throw an error or anything else and I'd rather not worry about that.

It would make the useful property that eval(repr(x)) == x for floating point numbers (currently, NameError: name 'inf' is not defined)

#

The last point is further explained on the example of trying to serialize a list of floats by storing its repr and then evaling it

#

currently, it will throw the NameError

hearty monolith Sep 5, 2020, 5:38 PM

#

Wait, which PEP is this?

sacred tinsel Sep 5, 2020, 5:52 PM

#

No PEP, it appears on the ideas mailing list: https://discordapp.com/channels/267624335836053506/704372456592506880/751487221374255115

red solar Sep 5, 2020, 6:16 PM

#

Ah ty 🙂

#

I agree with all of that, and hope it gets adopted (wonder how much code it would break tho)

#

Although ig if they added async as a keyword, they can do something for infinity

inland acorn Sep 5, 2020, 6:19 PM

#

I am guessing they would keep float("inf") and give a deprication warning for a few versions

teal yacht Sep 5, 2020, 6:22 PM

#

it shouldn't be deprecated tho

#

otherwise we should deprecate any cast from a literal

flat gazelle Sep 5, 2020, 6:24 PM

#

float("inf"), not float(some_variable_that_resolves_to_inf). In a similar vein 4(6) raises a syntax warning

raven ridge Sep 5, 2020, 6:35 PM

#

There'd be no reason to ever deprecate float("inf"), nor would this be a new keyword. It'd be a new builtin. Though assignments to inf would probably need to be banned, like they are for None and True and False, and that's backwards incompatible.

undone hare Sep 5, 2020, 6:36 PM

#

I don't think it should be deprecated tbh

torn charm Sep 5, 2020, 6:36 PM

#

anyone here a git genius?

undone hare Sep 5, 2020, 6:36 PM

#

You could make it assignable actually

#

You'd keep backward compatibility

flat gazelle Sep 5, 2020, 6:37 PM

#

Like NotImplemented

raven ridge Sep 5, 2020, 6:37 PM

#

At the cost of incongruity with the other builtin singletons.

flat gazelle Sep 5, 2020, 6:38 PM

#

Except NotImplemented

raven ridge Sep 5, 2020, 6:39 PM

#

TIL.

peak spoke Sep 5, 2020, 6:40 PM

#

Also Ellipsis

raven ridge Sep 5, 2020, 6:45 PM

#

If it's allowed to be reassigned, I don't see any backwards compatibility concerns.

noble birch Sep 5, 2020, 6:49 PM

#

is there a way to connect to the web via python (not like with sockets) to check for example if an URL exists?

zenith topaz Sep 5, 2020, 6:49 PM

#

What if I based my code on there being a possible nameerror on inf

noble birch Sep 5, 2020, 6:50 PM

#

what?

pliant tusk Sep 5, 2020, 6:50 PM

#

@noble birch requests

#

@zenith topaz then it wouldn’t be backwards compat

noble birch Sep 5, 2020, 6:50 PM

#

@pliant tusk i tried with urllib but it doesn't work

#

),:

pliant tusk Sep 5, 2020, 6:50 PM

#

What’s your goal?

noble birch Sep 5, 2020, 6:51 PM

#

to check if an URL exists

#

like try (function to connect to an URL) except print("URL doesn't exist")

pliant tusk Sep 5, 2020, 6:52 PM

#

Yea, use requests and catch the ConnectionError

noble birch Sep 5, 2020, 6:53 PM

#

how do i use requests?

#

is there a library to import?

pliant tusk Sep 5, 2020, 6:56 PM

#


def check_url(url):
  try:
    requests.get(url)
    return True
  except:
    return False

pearl river Sep 5, 2020, 6:57 PM

#

is there a library to import?
@noble birch yes, it's called requests 😛

radiant fulcrum Sep 5, 2020, 6:57 PM

#

you could just low key use the status code

#

its not gonna error

pearl river Sep 5, 2020, 6:58 PM

#

you'd also need to install it - requests is not a standard library.

Also, now that I notice, this is #internals-and-peps , not a help channel. Might want to move to one.

unkempt rock Sep 5, 2020, 6:59 PM

#

is there a library to import?
@noble birch

#

oops

#

i meant to say

#

that

#

you should go to your command promt and type ' pip install requests '

unkempt rock Sep 5, 2020, 7:19 PM

#

So basically my friend says he knows the least coding out of my Friend group is really hesitant to coding in general. Btw we’re all cs majors so how should I persuade him to code without being too preachy ??

📎 image0.png

feral cedar Sep 5, 2020, 7:20 PM

#

if you're all cs majors you probably shouldn't need motivation to code

unkempt rock Sep 5, 2020, 7:45 PM

#

if you're all cs majors you probably shouldn't need motivation to code
@feral cedar hmmm how so I’m just wondering

#

I guess it’s embedded into our cs instruction in college anyway

#

Well my friend Is the kind to get perfect scores on ap computer tests yet says he “forgot” all the code techniques when it comes to working on a project

raven ridge Sep 5, 2020, 7:51 PM

#

shrug he'll probably wind up dropping out or changing majors. Or focusing entirely on the math theory behind CS and never learn to code well. If he doesn't want to learn to code, you're not going to be able to talk him into it.

#

That's all off topic for this channel, though. #career-advice is probably the best channel for it.

unkempt rock Sep 5, 2020, 7:54 PM

#

shrug he'll probably wind up dropping out or changing majors. Or focusing entirely on the math theory behind CS and never learn to code well. If he doesn't want to learn to code, you're not going to be able to talk him into it.
@raven ridge no he says he wants to pick up on python and some js with discord.js but thru working with him in a casual group project , he has a really laissez faire approach and hardly ever intervenes unless the product looks “off” in his mind

pliant tusk Sep 5, 2020, 8:03 PM

#

@radiant fulcrum it errors for invalid urls (based on the dns response afaik)

pseudo cradle Sep 5, 2020, 8:46 PM

#

@unkempt rock Sounds like management material

unkempt rock Sep 5, 2020, 8:50 PM

#

Ye what if I should suggest my pap to go into business idk....he says he hasn’t really extrapolated too much into cs and/or programming in general. My friend actually put his work in progress cs50 certification on LinkedIn. He didn’t even finish it yet. Like he just does it for the resume so how should I tell him nicely? Sorry if I’m too concerned about his activity @pseudo cradle

frosty oyster Sep 6, 2020, 5:07 AM

#

Anyone around? I have a question about Python's hash() function and whether I should use an alternative.

charred barn Sep 6, 2020, 5:35 AM

#

what are you trying to do?

#

i'd not rely on the hash function for anything outside of implementing your own __hash__ methods.

mint forge Sep 6, 2020, 5:56 AM

#

How do I uninstall python 32 bit

charred barn Sep 6, 2020, 5:56 AM

#

#❓｜how-to-get-help

feral cedar Sep 6, 2020, 5:56 AM

#

just... uninstall it

mint forge Sep 6, 2020, 5:58 AM

#

it also has an change option can I use that to make it into 64 bit

feral cedar Sep 6, 2020, 5:59 AM

#

this isn't really the channel for this

#

see #❓｜how-to-get-help

teal stone Sep 6, 2020, 12:11 PM

#

What is the meaning of backtracking and how is it done?

@Beginner(slow-witted)

graceful saddle Sep 6, 2020, 12:52 PM

#

Hey Developers I am a 2nd year student and i want to build a system like jarvis of iron man. So i need your help I don't know where to start and what to do.

slim island Sep 6, 2020, 1:11 PM

#

This channel is usually a bit more focused and specific than that. Maybe an off topic channel would be better?

half wolf Sep 6, 2020, 1:50 PM

#

@graceful saddle so first you must revolutionize AI research :) Maybe scale down your ambition a bit.

lyric marsh Sep 6, 2020, 1:51 PM

#

can anyone send me a pygame code to make a space invaders game using pygame

boreal umbra Sep 6, 2020, 3:22 PM

#

Guido has this great hot take from 2002: "filter and map should die and be subsumed into list comprehensions"

odd ether Sep 6, 2020, 3:36 PM

#

@cunning scaffold this channel isn't the place for that

flat gazelle Sep 6, 2020, 3:45 PM

#

honestly, map(f,*a) is cleaner than (f(*v) for v in zip(*a)

sacred yew Sep 6, 2020, 4:37 PM

#

map is only good if the mapping is already a function

#

and not a lanbda

boreal umbra Sep 6, 2020, 4:41 PM

#

@flat gazelle it's more concise but I think the second one is a bit more obvious

#

granted both are entirely non-obvious if you're not familiar with that usage of the star operator.

#

I guess I wouldn't reject the first one if it was in a PR

#

I also use filter occasionally, but I feel like yield from filter(z, y) is more elegant than yield from (x for x in y if z)

teal yacht Sep 6, 2020, 4:57 PM

#

strong disagree on that comprehension being more obvious than the map, but we all have different tastes i guess

swift imp Sep 6, 2020, 5:07 PM

#

Is there a way to block child class from inheriting parent docstring?

#

At work we subclass DataFrames in a few cases and inheriting the docstring just makes the help so verbose

red solar Sep 6, 2020, 5:13 PM

#

Lol u reminded me of a case where someone was annoyed that docstring didn’t get inherited - i’ll ping u if I find it

#

(Although there’s probably easier ways)

grand crag Sep 6, 2020, 5:18 PM

#

If you control the parent class, override __init_subclass__ and set the child's __doc__ attribute to "". I've never tried it, but I think it could work.

#

>>> class T:
...     """This is a docstring"""
...     @classmethod
...     def __init_subclass__(cls, **kwargs):
...             cls.__doc__ = ""
...             super().__init_subclass__(**kwargs)
... 
>>> class M(T):
...     pass

class T(builtins.object)
 |  This is a docstring

class M(T)
``` It seems to work here. The docstring doesn't appear for `M`.

swift imp Sep 6, 2020, 5:42 PM

#

Nice, thanks!

dense needle Sep 6, 2020, 8:12 PM

#

hello !

#

can anyone help me i dont know how this code works i dont know the benefit of it

#

for i in range(len(supplies)):
       print('index'+ str(i) +'in supplies is :'+supplies[i])```

hasty thistle Sep 6, 2020, 8:55 PM

#

I'm assuming you got it from automate the boring stuff?

#

it's teaching you about loops, strings and indexing

dapper yoke Sep 6, 2020, 9:29 PM

#

Hello
Pls answer these both questions
How do I store the mid value of my string into a new matrix starting from 0,0 then 0,1 So on...

And

How do I store the values of a matrix into a list
Can I say x=[ [1][2],[3][4]]
Will x be having the 2 elements of my matrix?

boreal umbra Sep 6, 2020, 10:42 PM

#

@dapper yoke take a look at #❓｜how-to-get-help. This channel is specifically for discussion

dapper yoke Sep 6, 2020, 10:45 PM

#

Thankyou

torpid trellis Sep 7, 2020, 12:13 AM

#

anyone have any experience with boto3

trail ridge Sep 7, 2020, 2:35 AM

#

Hi, I just started learning about linked lists. I am printing what I stored in the linked list and the element at 0th index shows "None".

paper echo Sep 7, 2020, 3:00 AM

#

@trail ridge this sounds like a better question for #algos-and-data-structs . however you should at least show your code so that other people can help. nobody can guess what is wrong with your code

safe hedge Sep 7, 2020, 5:26 AM

#

Is the following an acceptable pattern:

class MyClass():
    def __init__(self, arg1, arg2, arg3, **kwargs):
        self.arg1 = arg1
        self.arg2 = arg2
        self.arg3 = arg3
        self.other_class = OtherClass(**kwargs)
        
    def __enter__(self):
        self.other_class.__enter__()
        return self
        
    def __exit__(self, exc_type, exc_value, traceback):
        self.cleanup_func()
        self.other_class.__exit__()

gritty pebble Sep 7, 2020, 5:30 AM

#

why wouldnt you subclass OtherClass

#

Though this probably should be in help #❓｜how-to-get-help

safe hedge Sep 7, 2020, 5:34 AM

#

Because this is just a really simplified version

#

Imagine if OtherClass was open(filename)

paper echo Sep 7, 2020, 5:35 AM

#

we've been kind of 50/50 on whether "is this pythonic" questions are allowed

#

as long as they're sophisticated and not "how do i write function"

safe hedge Sep 7, 2020, 5:35 AM

#

Yeah I felt this was more conceptual than a directed help

paper echo Sep 7, 2020, 5:36 AM

#

that said no i dont think there's anything wrong with it

#

there are lots of reasons why you wouldnt want to subclassOtherClass, e.g. maybe you have 3 other_class-like things

#

(the big problem i see here is lack of attrs usage 😉)

#

but for real yes its fine, however you should pass all those args in exit other_class.__exit__(exc_type, exc_value, traceback)

safe hedge Sep 7, 2020, 5:37 AM

#

Yeah I realised that after

#

What exactly would attrs do here though?

paper echo Sep 7, 2020, 5:38 AM

#

im also not a fan of the **kwargs here

#

class MyClass():
    def __init__(self, arg1, arg2, arg3, other_thing: OtherClass):
        self.arg1 = arg1
        self.arg2 = arg2
        self.arg3 = arg3
        self.other_thing = other_thing
        
    def __enter__(self):
        self.other_thing.__enter__()
        return self
        
    def __exit__(self, exc_type, exc_value, traceback):
        self.cleanup_func()
        self.other_thing.__exit__()

#

actually attrs isnt that useful unless you want type annotations, in which case it saves you a lot of duplicated typing

safe hedge Sep 7, 2020, 5:39 AM

#

I wouldn't normally use kwargs. Again I was trying to create a really generic example

paper echo Sep 7, 2020, 5:40 AM

#

@attr.s
class MyClass():
    arg1: int = attr.ib()
    arg2: float = attr.ib()
    arg3: bool = attr.ib()
    other_thing: OtherClass = attr.ib()
        
    def __enter__(self):
        self.other_thing.__enter__()
        return self
        
    def __exit__(self, exc_type, exc_value, traceback):
        self.cleanup_func()
        self.other_thing.__exit__()

safe hedge Sep 7, 2020, 5:40 AM

#

I'm unsure on whether it's better to allow someone to pass the composite class or create it within the init

paper echo Sep 7, 2020, 5:40 AM

#

i definitely prefer the former. you can always create a default one if they pass None

safe hedge Sep 7, 2020, 5:41 AM

#

For example in a situation where the composite class is something you wouldn't expect the end-user to ever directly interact with

paper echo Sep 7, 2020, 5:41 AM

#

fair enough. if the wrapped class is never meant to be created on its own then it's fine

#

plus creating classes to pass as parameters to other classes feels very clunky and Java-esque so i don't blame you for wanting to avoid it

#

but sometimes it really is the best way to do things

#

i'll take clunkiness if it means avoiding wasteful code duplication

#

or if it means avoiding a kwarg dumpster

#

i really dont like **kwargs in user-facing functions unless it's very obvious what said kwargs are being passed to

safe hedge Sep 7, 2020, 5:44 AM

#

I have one case where there is a sort of 1-1 mapping of inner class to wider class, but which inner class you want is dependent on the outer class. Does that make sense at all haha

paper echo Sep 7, 2020, 5:44 AM

#

hm

#

why

#

maybe something like this?

@attr.s
class MyHttpxClient:
    sansio_client: MyClient = attr.ib()
    httpx_client: httpx.Client = attr.ib(factory=httpx.Client)

safe hedge Sep 7, 2020, 5:45 AM

#

Like, I have a generic outer and generic inner. But then I have a specialised outer which uses a subclassed inner with one method overidden

paper echo Sep 7, 2020, 5:45 AM

#

can't the outer just wrap the one special method

#

instead of making a whole customized version of the inner

safe hedge Sep 7, 2020, 5:46 AM

#

The outer class would then override a method on a class it's being passed?

paper echo Sep 7, 2020, 5:46 AM

#

no of course not

safe hedge Sep 7, 2020, 5:48 AM

#

Like:

class InnerA():
   ...

class InnerB(InnerA):
    def overridden(self):
         #stuff

class OuterA():
    def __init__(...):
        self.inner = InnerA()

class OuterB(OuterA):
    def __init__()
         self.inner = InnerB()

#

Does that explain what I'm talking about?

paper echo Sep 7, 2020, 5:48 AM

#

@attr.s()
class OuterThing:
    inner_thing: InnerThing = attr.ib()

    def frobulate(self, x: float) -> float:
        return self.inner_thing.frobulate(x / 100.0)

versus

class SpecialInnerThing(InnerThing):
    def frobulate(self, x: float) -> float:
        return super().frobulate(x / 100.0)

class OuterThing:
    inner_thing: SpecialInnerThing
    def __init__(self):
        self.inner_thing = SpecialInnerThing()

    def frobulate(self, x: float) -> float:
        return self.inner_thing.frobulate(x)

safe hedge Sep 7, 2020, 5:50 AM

#

I think what I probably want is for the outer class to define an inner class factory?

paper echo Sep 7, 2020, 5:51 AM

#

maybe. which in python of course is just a class

#

it really depends on how your application is set up

#

consider what your public interfaces are

#

what your data contracts are

woven apex Sep 7, 2020, 6:14 AM

#

hi everyone

wide shuttle Sep 7, 2020, 6:15 AM

#

Hello Nurken

woven apex Sep 7, 2020, 6:19 AM

#

does anyone know, how to create paint program at Python?

wide shuttle Sep 7, 2020, 6:28 AM

#

That's not really a question for this channel; we try to reserve this channel for discussing the Python programming language itself, from a higher-level and more abstract perspective.

#

We do have a lot of other channels where you can ask your question, like #python-discussion, or help channels

gleaming rover Sep 7, 2020, 6:29 AM

#

plus creating classes to pass as parameters to other classes feels very clunky and Java-esque so i don't blame you for wanting to avoid it
@paper echo why do you think so?

woven apex Sep 7, 2020, 6:29 AM

#

oh sorry

paper echo Sep 7, 2020, 6:30 AM

#

@gleaming rover it's just not something you see often in python

#

and classes like BeanFactoryFactory are a meme

gleaming rover Sep 7, 2020, 6:33 AM

#

@gleaming rover it's just not something you see often in python
@paper echo wait, let me clarify

#

did you mean classes, as in type objects (as opposed to instances)?

paper echo Sep 7, 2020, 6:34 AM

#

no sorry i mean instances, but things like this OuterThing(InnerThing(a, b), c)

gleaming rover Sep 7, 2020, 6:34 AM

#

oh hm

#

isn't that basically dependency injection

paper echo Sep 7, 2020, 6:34 AM

#

yes

gleaming rover Sep 7, 2020, 6:35 AM

#

I actually don't have much Java experience so I'm not sure about that part of your statement, but why do you think it's clunky

paper echo Sep 7, 2020, 6:35 AM

#

i dont have much java experience either so i might be treating it unfairly

#

its clunky because you just dont see it that often in libraries

#

but i think its a perfectly valid, maybe even underused, pattern

gleaming rover Sep 7, 2020, 6:36 AM

#

hm.

#

now that you mention it

#

why is dependency injection so uncommon in Python

#

or is it just in the stuff I use

paper echo Sep 7, 2020, 6:36 AM

#

(fwiw i dont like dependency injection, id rather just wrap stuff)

#

you see things like factory= very occasionally

#

but again why do that when you can just write a wrapper function

#

its a good question though

unkempt rock Sep 7, 2020, 6:38 AM

#

Whats future module?

safe hedge Sep 7, 2020, 6:39 AM

#

It's composition

#

Personally I prefer composition to inheritance where possible

gleaming rover Sep 7, 2020, 6:39 AM

#

Whats future module?
@unkempt rock basically, a way to apply changes that will be mandatory in a future version of Python, but optional in the one you're running

unkempt rock Sep 7, 2020, 6:39 AM

#

Oh

raven ridge Sep 7, 2020, 6:48 AM

#

future, or __future__ ?

#

__future__ is part of the Python language, a way to opt into backwards incompatible language changes before they become mandatory. future is a 3rd party module that tries to help you write code compatible with both Python 2 and Python 3.

deft pagoda Sep 7, 2020, 7:04 AM

#

and a Future is...

raven ridge Sep 7, 2020, 7:07 AM

#

entirely different, but that's in futures, not future or __future__, heh

unkempt rock Sep 7, 2020, 8:01 AM

#

I want to override gettattr but my mul does a deepcopy which causes gettattr to throw an error. I don't want to override deepcopy as I don't feel I can reliably duplicate what that does. Anyone know if there's another solution?

brittle yew Sep 7, 2020, 8:04 AM

#

anyone here use buildozer???

wide shuttle Sep 7, 2020, 8:07 AM

#

@unkempt rock Does your __getattr__ raise an AttributeError for nonexisting attributes? If not, that's probably what's causing the issue you have.

#

Normally, when you access a non-existing attribute, you'll get an AttributeError. However, if you overwrite __getattr__, that method gets called and it returns something. If the function does not hit an explicit return, it will return None implicitly. Take a look at this:

#

!e

class Foo:

    def __getattr__(self, attr):
        if attr == "bar":
            return "some result"


f = Foo()
print(f"This will print 'some result' as expected: {f.bar!r}")
print(f"This will print `None`: {f.something_else!r}")

fallen slateBOT Sep 7, 2020, 8:08 AM

#

@wide shuttle :white_check_mark: Your eval job has completed with return code 0.

001 | This will print 'some result' as expected: 'some result'
002 | This will print `None`: None

wide shuttle Sep 7, 2020, 8:09 AM

#

I think this is what happening in your case

#

If you raise an AttributeError, copy.deepcopy will not complain:

#

!e

import copy


class Foo:

    def __getattr__(self, attr):
        if attr == "bar":
            return "some result"

        raise AttributeError

f = Foo()
copy.deepcopy(f)

fallen slateBOT Sep 7, 2020, 8:10 AM

#

@wide shuttle :warning: Your eval job has completed with return code 0.

[No output]

unkempt rock Sep 7, 2020, 8:11 AM

#

hmm. now i get max recurision.

#

def getattr(self, key):
if key in self.kwargs.keys():
return self.kwargs[key]
else:
# return None
raise AttributeError

#

but the deepcopy error is gone. however now it wont deep copy

peak spoke Sep 7, 2020, 8:13 AM

#

You have to use the attribute access from a parent class that doesn't modify it or it'll call itself every time

unkempt rock Sep 7, 2020, 8:14 AM

#

i thought raising the attribute error stopped that?

#

or was supposed to

deft pagoda Sep 7, 2020, 8:15 AM

#

self.kwargs <- if kwargs isn't an attribute you'll be calling getattr again

unkempt rock Sep 7, 2020, 8:16 AM

#

sorry . yes probably not best name. but it is defined on init

#

and just takes the kwargs that are passed

wide shuttle Sep 7, 2020, 8:16 AM

#

In this case, the object won't be initialized using teh __init__, so that attribute won't exist (yet)

#

So, everytime it's trying to check if an attribute exists before that kwargs becomes available, it will get in a __getattr__ loop

#

Maybe if you do it like this (or handle the KeyError), it will work:

    def __getattr__(self, attr):
        kwargs = super().__getattribute__('kwargs')
        if attr in kwargs:
            return kwargs[attr]

        raise AttributeError

unkempt rock Sep 7, 2020, 8:18 AM

#

class MyClass(object):
def init(self, *args, **kwargs):
self.args = args
self.kwargs = kwargs

def __mul__(self, other):
    reproducer = []
    for i in range(other):
        reproducer.append(copy.deepcopy(self))
    return reproducer

def __getattr__(self, key):
    if key in self.kwargs.keys():
        return self.kwargs[key]
    else:
        # return None
        raise AttributeError

#

ive deleted some stuff

#

but essentiall i want my cake and eat it

#

i feel if i wrote a deepcopy that did what deep copy does. it may work. but i dont trust i can do that

wide shuttle Sep 7, 2020, 8:19 AM

#

And the suggestion I gave above?

#

Does that work?

unkempt rock Sep 7, 2020, 8:20 AM

#

essentially if prop not exist. look for it on the nest array. gonna try your tip now. 5 mins

#

woah!

#

5 hours last night 😦 then i gave up

#

thank you so much

#

incredible

#

thank you so much . i've read the code and completely understand now what you are doing. I don't know why that wasn't obvious to me. thanks

deft pagoda Sep 7, 2020, 8:24 AM

#

I'm pretty sure I've burned myself with getattr a few times

wide shuttle Sep 7, 2020, 8:25 AM

#

For me, it's partly because None is just a valid, regular return value that's returned implicitly. My first instinct is to write a __getattr__ that just handles the dynamic attributes that I want to handle, but, if you're not careful, now every attribute exists dynamically but most of them just return None.

#

You don't notice this a lot until you hit something that relies on that AttributeError signal to be raised.

#

And, in this case, deepcopy throws a curveball as well, as you'd expect kwargs to exist from the start but it only exists after it's been deepcopied.

unkempt rock Sep 7, 2020, 8:28 AM

#

can i credit you?

#

link to ur blog or something on the code comment

#

?

wide shuttle Sep 7, 2020, 8:31 AM

#

I don't really have anything to link to. Most of the free time I have for Python I spend on this community.

#

And I don't particularly need to get credit, as it were just a few lines and I integrated @peak spoke idea as well

unkempt rock Sep 7, 2020, 8:34 AM

#

big thanks to all that helped. I'll link the discord group. very grateful

#

I cant now get dot notation on extra props. which is so cool

#

*can

stuck barn Sep 7, 2020, 8:38 AM

#

how do i call a function given as a parameter

peak spoke Sep 7, 2020, 8:38 AM

#

hexed maple Sep 7, 2020, 8:40 AM

#

@stuck barn wdym
like a callback ?

stuck barn Sep 7, 2020, 8:41 AM

#

you would do myFunc(func) and it executes the function func

#

thats what i need

unkempt rock Sep 7, 2020, 8:41 AM

#

func()

hexed maple Sep 7, 2020, 8:42 AM

#

ok

stuck barn Sep 7, 2020, 8:42 AM

#

it executes the parameter

#

which can vary

hexed maple Sep 7, 2020, 8:43 AM

#

u are passing the func by name (Func("func")) or the object itself (Func(func))

stuck barn Sep 7, 2020, 8:43 AM

#

yes

hexed maple Sep 7, 2020, 8:44 AM

#

i mean how are u passing it
like Func("func") or Func(func)

stuck barn Sep 7, 2020, 8:44 AM

#

second one

#

@hexed maple

hexed maple Sep 7, 2020, 8:50 AM

#

ok

raven ridge Sep 7, 2020, 8:51 AM

#

Python has functions as first order objects. You can pass a function just like passing any other variable. Any variable that holds a function can just be called like a function.

hexed maple Sep 7, 2020, 8:51 AM

#

^^

stuck barn Sep 7, 2020, 8:51 AM

#

wait so if i do h = func then i can do h() ?

unkempt rock Sep 7, 2020, 8:52 AM

#

h = func

raven ridge Sep 7, 2020, 8:52 AM

#

!e ```python
x = print
x("hello")

def say_hi(printer):
printer("hi")
say_hi(print)

fallen slateBOT Sep 7, 2020, 8:52 AM

#

@raven ridge :white_check_mark: Your eval job has completed with return code 0.

001 | hello
002 | hi

stuck barn Sep 7, 2020, 8:52 AM

#

yes i saw that

#

typo

wide shuttle Sep 7, 2020, 8:52 AM

#

@peak spoke SO does list a license for user contributions, but some examples and snippets are fairly generic. I doubt you could really claim "copyright" on them. Anyway, we're getting a bit off-topic, but you're right about people probably not expecting credit.

unkempt rock Sep 7, 2020, 8:52 AM

#

Although you could do h = func() if func() returned another function

hexed maple Sep 7, 2020, 8:53 AM

#

!e

fallen slateBOT Sep 7, 2020, 8:53 AM

#

You are not allowed to use that command here. Please use the #bot-commands channel instead.

hexed maple Sep 7, 2020, 8:53 AM

#

ohh

#

here is a very simple example

def a(func):
    if callable(func):
        func()
    else:
        pass
def b():
    print("it works")

a(b)
#this wont
a("hi")

raven ridge Sep 7, 2020, 8:53 AM

#

it's a staff superpower to use !e in discussion channels.

hexed maple Sep 7, 2020, 8:53 AM

#

i shall wield it someday

raven ridge Sep 7, 2020, 8:57 AM

#

@stuck barn for completeness's sake: a function is an object. That object is able to be called. The name of the variable that refers to that object is irrelevant. The statement def foo(...): creates a new function object and assigns it to the name foo. It's syntactic sugar for a regular assignment. Once it has been assigned, it can be reassigned to a new name, or passed as an argument, or whatever.

deft pagoda Sep 7, 2020, 8:57 AM

#

I wish there was a std library of common decorators

raven ridge Sep 7, 2020, 8:58 AM

#

It's the function object itself that has something magical about it - callability - not the original name that it was defined with. The only thing special about the name that it was defined with is that it's stored and introspectable, but that's really only for debugging purposes and to give a nice repr

half wolf Sep 7, 2020, 10:18 AM

#

The nice repr is hugely important though. I really wish lambdas had reasonable reprs.

gritty pebble Sep 7, 2020, 11:58 AM

#

It would be cool if there was a bitset/bitarray in the standard library

undone hare Sep 7, 2020, 11:58 AM

#

What about

#

!d array.array

fallen slateBOT Sep 7, 2020, 11:58 AM

#

`array.array`

class array.array(typecode[, initializer])```
A new array whose items are restricted by *typecode*, and initialized from the optional *initializer* value, which must be a list, a [bytes-like object](../glossary.html#term-bytes-like-object), or iterable over elements of the appropriate type.

If given a list or string, the initializer is passed to the new array’s [`fromlist()`](#array.array.fromlist "array.array.fromlist"), [`frombytes()`](#array.array.frombytes "array.array.frombytes"), or [`fromunicode()`](#array.array.fromunicode "array.array.fromunicode") method (see below) to add initial items to the array. Otherwise, the iterable initializer is passed to the [`extend()`](#array.array.extend "array.array.extend") method.

Raises an [auditing event](sys.html#auditing) `array.__new__` with arguments `typecode`, `initializer`.

undone hare Sep 7, 2020, 11:59 AM

#

bytearray is also a thing

gritty pebble Sep 7, 2020, 12:03 PM

#

That's not the same thing

#

https://pypi.org/project/bitarray/ like this

PyPI

bitarray

efficient arrays of booleans -- C extension

undone hare Sep 7, 2020, 12:05 PM

#

You could make an array of bool

#

Probably not that efficient, but still

gritty pebble Sep 7, 2020, 12:08 PM

#

Yeah, the use case where I could have used something like this I ended up using bytearray which was much better then a list

#

Imo it seems like something that would fit nicely in collections but I'm not sure if it's too niche of a data type

mighty viper Sep 7, 2020, 2:35 PM

#

can i host online socket server from heroku

#

to send and recv data from the server

boreal umbra Sep 7, 2020, 2:57 PM

#

@mighty viper I would ask in #web-development

south egret Sep 7, 2020, 4:49 PM

#

📎 E.PNG

#

WHy am i getting this error?

#

if i shutdown and restart then it works

#

but am not understanding why am i getting this error

pallid meteor Sep 7, 2020, 4:52 PM

#

its not an error

#

the cells are running

#

also, this isnt the proper channel to ask about this

south egret Sep 7, 2020, 4:52 PM

#

ok

#

Still can u tell me why when i click on run it doesnt work

charred wagon Sep 7, 2020, 4:54 PM

#

Maybe, if you first move to the right channel. see #❓｜how-to-get-help

timber bobcat Sep 7, 2020, 5:42 PM

#

Ayo anyone knows if there any way to implement a key of some sort to only be able to run ur python script on one computer ? Let's say for example i put a program for sale and i dont want it to just be passed on so easily is there a way i can add something to my program to only run on that particular computer ?

half wolf Sep 7, 2020, 5:47 PM

#

There are many ways. The best way is of course to not ship your software at all and instead have it on your own server. After that you should use a compiled language, then if you finally decide to use python then it's super easy to bypass and you should learn to live with that.

paper echo Sep 7, 2020, 5:48 PM

#

Can you even do that in a compiled language

boreal umbra Sep 7, 2020, 5:48 PM

#

@timber bobcat you can use PyArmor, but it's not likely that anyone will want to claim credit for your exact code.

paper echo Sep 7, 2020, 5:48 PM

#

I think their concern is piracy

boreal umbra Sep 7, 2020, 5:48 PM

#

Ah

timber bobcat Sep 7, 2020, 5:51 PM

#

yeah i already considered PyArmor so they cant read the files , but my concern is that one guy buys it and he just spreads it like covid-19

#

i was wondering if there was a way to make the program only run on one computer

paper echo Sep 7, 2020, 5:52 PM

#

No matter what language you use, basically the only way to stop that is to use a one time registration key

#

Consider that even professional and very expensive software like Adobe creative suite and Microsoft word can be cracked

timber bobcat Sep 7, 2020, 5:52 PM

#

yea i know

#

well that sounds interesing the one time registration key

grave jolt Sep 7, 2020, 5:53 PM

#

or use the Software As A Service model

paper echo Sep 7, 2020, 5:53 PM

#

I'm actually not entirely sure how license keys work for software like that. I suppose the license key is sent to a server for approval, and then some kind of local confirmation of approval is stored

#

Or you can have the program connect to the Internet to check the key upon start up

#

At which point yes, it becomes much easier to hack apart a python program than a compiled C++ program in order to get it to run without a valid key..

#

I also think that kind of start up check can result in being user hostile as it now requires an Internet connection in order to use the software

grave jolt Sep 7, 2020, 5:54 PM

#

You could cache the check

timber bobcat Sep 7, 2020, 5:55 PM

#

my program needs internet anyways to run

paper echo Sep 7, 2020, 5:55 PM

#

Maybe there are algorithms that let you use some kind of asymmetric encryption

timber bobcat Sep 7, 2020, 5:55 PM

#

so it wont be a problem really

#

but tbh i dont think someone will go out of their way to crack my program if i implement a one time registration key

#

its just a bot for a phone game

grave jolt Sep 7, 2020, 5:56 PM

#

that sounds ToS-breaking 🤔

timber bobcat Sep 7, 2020, 5:56 PM

#

shhhh

grave jolt Sep 7, 2020, 5:57 PM

#

Yeah, selling an automation bot for a game definitely sounds ToS-breaking

paper echo Sep 7, 2020, 5:57 PM

#

!rules 5

fallen slateBOT Sep 7, 2020, 5:57 PM

#

Rules

5. Do not provide or request help on projects that may break laws, breach terms of services, be considered malicious/inappropriate or be for graded coursework/exams.

timber bobcat Sep 7, 2020, 5:57 PM

#

oh shiii👀

paper echo Sep 7, 2020, 5:57 PM

#

Seems a bit ironic to worry about piracy when you're botting someone else's application

grave jolt Sep 7, 2020, 5:59 PM

#

lmao

#

well, criminals wear body armor, right

paper echo Sep 7, 2020, 6:00 PM

#

True

timber bobcat Sep 7, 2020, 6:01 PM

#

well sorry for that one lads

#

kinda got overwhelmed and forgot bout the rules

vast dome Sep 7, 2020, 6:01 PM

#

hi

timber bobcat Sep 7, 2020, 6:01 PM

#

sup

vast dome Sep 7, 2020, 6:01 PM

#

i joined

#

is this the general chat?

timber bobcat Sep 7, 2020, 6:02 PM

#

the one above this one

vast dome Sep 7, 2020, 6:02 PM

#

ok thanks but i think ill stay here

timber bobcat Sep 7, 2020, 6:02 PM

#

📎 1.png

#

that one

vast dome Sep 7, 2020, 6:03 PM

#

anyways u should set a pic if u want i could search one for ya

#

welp-

timber bobcat Sep 7, 2020, 6:03 PM

#

naahh thanks im coo

vast dome Sep 7, 2020, 6:03 PM

#

imma just go read rules

#

#rules to be faster sorry hehe

timber bobcat Sep 7, 2020, 6:04 PM

#

i think we should move to the general chat till the mods dont throw the mighty ban hammer uppon us

vast dome Sep 7, 2020, 6:06 PM

#

kk

paper echo Sep 7, 2020, 6:06 PM

#

@vast dome thanks for reading them, a lot of people dont even bother

#

(Not throwing shade)

vast dome Sep 7, 2020, 6:06 PM

#

🙂

timber bobcat Sep 7, 2020, 6:07 PM

#

ayy man i read em

paper echo Sep 7, 2020, 6:07 PM

#

And yes @timber bobcat thank you as well

timber bobcat Sep 7, 2020, 6:07 PM

#

just got a bit carried away

paper echo Sep 7, 2020, 6:07 PM

#

Wasnt meant to be a jab at you

timber bobcat Sep 7, 2020, 6:07 PM

#

oh

paper echo Sep 7, 2020, 6:08 PM

#

Lots of people just ignore the rules and sometimes get upset when they are directed to the rules

#

You didnt do that so its all good

timber bobcat Sep 7, 2020, 6:10 PM

#

oh yea i know people that do get hella angry

#

but im calm and understanding

supple karma Sep 7, 2020, 6:21 PM

#

Hey my RTX 2060 is sitting at 60% usage while training a tensorflow bot. Why is tensorflow not maxing my card?

#

Latest version*

radiant fulcrum Sep 7, 2020, 6:22 PM

#

because you're training AI and thats inherently load intensive

#

TF is doing what its supposed todo by making use of your GPU

supple karma Sep 7, 2020, 6:24 PM

#

Oh. But surely it should use all of it?

radiant fulcrum Sep 7, 2020, 6:27 PM

#

Normally other limitation

#

RAM, CPU bottle knecking it probably

supple karma Sep 7, 2020, 6:28 PM

#

Hmm interesting. 🤔

radiant fulcrum Sep 7, 2020, 6:28 PM

#

but equally you should remember the system GPU's like that are designed for are not the same as those used for AI

supple karma Sep 7, 2020, 6:28 PM

#

CPU and system RAM is cool.
True. Very true.

radiant fulcrum Sep 7, 2020, 6:29 PM

#

VRam aswell can be a limit

supple karma Sep 7, 2020, 6:29 PM

#

Thats on 97%...

#

So that's probably why.

#

Wait nvm its on 37% weird

boreal umbra Sep 7, 2020, 7:04 PM

#

try:
    from scipy.stats import binom_test
except ImportError:
    print >>sys.stderr, 'INFO: Could not import scipy (www.scipy.org): signtest is not available.'

#

this was apparently written in 2013

#

has that syntax for print ever been supported or does this person just think they're writing C++?

peak spoke Sep 7, 2020, 7:06 PM

#

https://docs.python.org/2.7/reference/simple_stmts.html#the-print-statement

boreal umbra Sep 7, 2020, 7:06 PM

#

so this is python 2?

peak spoke Sep 7, 2020, 7:07 PM

#

that line at least

boreal umbra Sep 7, 2020, 7:07 PM

#

I have a few good things to say about this file

#

for example, the author uses random.choice

grave jolt Sep 7, 2020, 7:28 PM

#

that's some weird syntax 👀

peak spoke Sep 7, 2020, 8:58 PM

#

I've made a config system for my app where values are accessed and set with class attribute access on classes directly at the module level so with the class

class Category:
    value: ... = ...

I can access the shared value from every module in my app with an import and all value gets synced to a file when set unless a method is used to delay it.
This works great, but I'm not sure about the design with classes and attributes, do you think it's fine or since the values are being modified at runtime some kind of an instance that gets passed around would be more fitting?

spark venture Sep 7, 2020, 9:32 PM

#

how do i extract the most dominant color from any type of image in any format?

#

somewhat like spotify

unkempt rock Sep 7, 2020, 10:01 PM

#

This isn't the place for questions, but https://stackoverflow.com/questions/3241929/python-find-dominant-most-common-color-in-an-image here

Stack Overflow

Python - Find dominant/most common color in an image

I'm looking for a way to find the most dominant color/tone in an image using python. Either the average shade or the most common out of RGB will do. I've looked at the Python Imaging library, and c...

#

for example, the author uses random.choice
@boreal umbra is random.choice bad?

spark venture Sep 7, 2020, 10:13 PM

#

thanks @unkempt rock!

boreal umbra Sep 7, 2020, 10:18 PM

#

@unkempt rock no, random.choice is very good

#

The alternative is to use randint for the length of your list

unkempt rock Sep 7, 2020, 10:24 PM

#

ah ok

boreal umbra Sep 7, 2020, 10:37 PM

#

@unkempt rock (my responses are intermittent because I'm at work) random.choice is also better because it works for any container type. I think.

#

Let's see.

unkempt rock Sep 7, 2020, 10:38 PM

#

No worries. I'll read your responses as they come.

boreal umbra Sep 7, 2020, 10:38 PM

#

!e

bob = {1, 2, 3, 4, 5}
from random import choice
print(choice(bob))

fallen slateBOT Sep 7, 2020, 10:38 PM

#

@boreal umbra :x: Your eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "<string>", line 3, in <module>
003 |   File "/usr/local/lib/python3.8/random.py", line 291, in choice
004 |     return seq[i]
005 | TypeError: 'set' object is not subscriptable

boreal umbra Sep 7, 2020, 10:39 PM

#

Omg

#

It doesn't work for sets.

#

I'm so upset

burnt obsidian Sep 7, 2020, 10:39 PM

#

Hey guys, I'm using the Youtube API Data
and i came to this error

googleapiclient.errors.HttpError: <HttpError 403 when requesting https://www.googleapis.com/youtube/v3/channels?part=id&forUsername=ItsAleMazing&key=AIzaSyAM3YG7QAGmwiz36vKksbalOwKFKGisxVk%0A&alt=json returned "The request cannot be completed because you have exceeded your <a href="/youtube/v3/getting-started#quota">quota</a>.">

my code:

        addLog('(type=id) Getting a request of Channel ID of "' +  username + '" ...')
        time.sleep(5)
        request = youtube.channels().list(
                                            part="id",
                                            forUsername=username
                                        )
        addLog('(type=id) Got a request of Channel ID of "' + username + '" ...')
        
        addLog('(type=id) Executing the Request of "youtube.activities" of [' + username +']...')
        time.sleep(5)
        response = request.execute()
        time.sleep(5)```

May someone help me ?
the error come from this line  `response = request.execute()`

boreal umbra Sep 7, 2020, 10:39 PM

#

@burnt obsidian this channel is specifically for discussions. Take a look at #❓｜how-to-get-help

feral cedar Sep 7, 2020, 10:45 PM

#

steler it works on sequences

solemn jewel Sep 7, 2020, 10:50 PM

#

hey so for matplotlib.pyplot why do i have to call plt.show()? can't it just pop up automatically for me?

gleaming rover Sep 7, 2020, 10:51 PM

#

hey so for matplotlib.pyplot why do i have to call plt.show()? can't it just pop up automatically for me?
@solemn jewel depends on where you're running it

#

some environments do, automatically

#

e.g. if you're running in terminal

#

it doesn't

#

so that you can apply all your changes before you show

#

not really the right channel btw, try #data-science-and-ml

solemn jewel Sep 7, 2020, 10:54 PM

#

oh ok

#

sorry

unkempt rock Sep 7, 2020, 10:55 PM

#

Its weird that random.choice doesnt work on sets

feral cedar Sep 7, 2020, 10:56 PM

#

not really

gleaming rover Sep 7, 2020, 10:57 PM

#

well, if the container is unordered, you don't really have a way to get an element that you can prove is random

unkempt rock Sep 7, 2020, 10:57 PM

#

Makes sense

feral cedar Sep 7, 2020, 10:57 PM

#

it needs a sequence

unkempt rock Sep 7, 2020, 10:58 PM

#

A set is really more like a dictionary with just keys I guess

charred wagon Sep 7, 2020, 11:04 PM

#

I imagine random.choice gets a random integer in the range of the sequence length and uses that as the index to get a random element. Don't know if that's actually true

#

That's always been my explanation to myself for why things likes sets will not work

ebon jasper Sep 7, 2020, 11:05 PM

#

probably, sounds about right

#

not sure if this is the right channel but, how do you write a function that can clear frames in tkinter?

gleaming rover Sep 7, 2020, 11:07 PM

#

not sure if this is the right channel but, how do you write a function that can clear frames in tkinter?
@ebon jasper #user-interfaces

ebon jasper Sep 7, 2020, 11:07 PM

#

thanks

cursive gazelle Sep 7, 2020, 11:07 PM

#

I imagine random.choice gets a random integer in the range of the sequence length and uses that as the index to get a random element. Don't know if that's actually true
@charred wagon this is true

boreal umbra Sep 7, 2020, 11:18 PM

#

steler it works on sequences
@feral cedar I can understand based on the error message why the implementation doesn't work for sets, but conceptually getting a random item from a set isn't hugely different from getting one from a list.

gleaming rover Sep 7, 2020, 11:19 PM

#

@feral cedar I can understand based on the error message why the implementation doesn't work for sets, but conceptually getting a random item from a set isn't hugely different from getting one from a list.
@boreal umbra is it not...?

boreal umbra Sep 7, 2020, 11:19 PM

#

The very concept of getting a random item from an ordered sequence is agnostic to the fact that that sequence is ordered.

gleaming rover Sep 7, 2020, 11:20 PM

#

in particular, for a set, there is no way to refer to any specific element

boreal umbra Sep 7, 2020, 11:20 PM

#

Right

gleaming rover Sep 7, 2020, 11:21 PM

#

it's not about it being ordered, really, I think

boreal umbra Sep 7, 2020, 11:22 PM

#

Sets have a method that will return a random element and remove it from the set. I don't remember the name for sure but it might be pop.

gleaming rover Sep 7, 2020, 11:23 PM

#

Sets have a method that will return a random element and remove it from the set. I don't remember the name for sure but it might be pop.
@boreal umbra it is pop, but it doesn't return a random element

#

it returns an arbitrary element

boreal umbra Sep 7, 2020, 11:24 PM

#

Point taken.

safe hedge Sep 8, 2020, 12:25 AM

#

Thinking a bit more about the discussions I had in here yesterday with __enter__ and __exit__, is there some guidance for how an object with those defined is meant to behave. Like it seems that there is not consistency since with can be used without as i.e. with threading.Lock():. Is it really just a case of good documentation to ensure the correct usage of your class with a context manager?

sacred yew Sep 8, 2020, 12:26 AM

#

usually it should be somewhat obvious when you need as

#

since that's when you actually want to use the object

spark magnet Sep 8, 2020, 1:18 AM

#

@safe hedge the only semantic is that __enter__ should will be called on entering, and __exit__ on exiting. it can be used for resource acquisition, or exception management, or other things.

safe hedge Sep 8, 2020, 1:29 AM

#

@spark magnet So effectively yes any specific usage/behaviour is only really covered by documenting?

#

e.g. Like this from stdlib https://docs.python.org/3/library/threading.html#using-locks-conditions-and-semaphores-in-the-with-statement

paper echo Sep 8, 2020, 6:58 AM

#

yes @safe hedge

unkempt rock Sep 8, 2020, 11:27 AM

#

hey guys

warm spire Sep 8, 2020, 11:28 AM

#

sup

unkempt rock Sep 8, 2020, 2:16 PM

#

Hi

#

I need help

undone hare Sep 8, 2020, 2:17 PM

#

Hey, see #❓｜how-to-get-help

#

lemon_pleased

unkempt rock Sep 8, 2020, 7:05 PM

#

why hasattr func even exists ?
can't we just use getattr and compare if its something or not ?

sacred yew Sep 8, 2020, 7:06 PM

#

compatibility probably

#

python has a lot of builtin functions

paper echo Sep 8, 2020, 7:09 PM

#

@unkempt rock because then you have to always decide on a sentinel value

modern night Sep 8, 2020, 7:10 PM

#

@unkempt rock you could do getattr(obj, attr_name, None) but if the object does have that attribute and its value is just None you will get false positives you need a default for your method and there is always a chance that that object has that value as its atribute

paper echo Sep 8, 2020, 7:10 PM

#

hasattr is also implemented directly in C

#

https://github.com/python/cpython/blob/c96d00e88ead8f99bb6aa1357928ac4545d9287c/Python/bltinmodule.c#L1131-L1150 this is a lot more efficient than, say getattr(obj, attr_name, SENTINEL) is SENTINEL

GitHub

python/cpython

The Python programming language. Contribute to python/cpython development by creating an account on GitHub.

#

and a lot less ugly

radiant fulcrum Sep 8, 2020, 7:13 PM

#

@paper echo only thing with hasattr compared todoing it with getattr is that it wont get methods

#

from what ive found

modern night Sep 8, 2020, 7:13 PM

#

class Foo:
    def bar(self):
        ...

        
hasattr(Foo(), 'bar')
True```works for me

radiant fulcrum Sep 8, 2020, 7:13 PM

#

hmm

paper echo Sep 8, 2020, 7:14 PM

#

what do you mean it wont get methods?

radiant fulcrum Sep 8, 2020, 7:14 PM

#

idk now lol, ive had issues in the paste where it wont get methods without doing say bar()

paper echo Sep 8, 2020, 7:14 PM

#

!e ```python
class Foo:
def bar(self):
...

foo = Foo()
print(type(getattr(Foo, 'bar')))
print(type(getattr(foo, 'bar')))

fallen slateBOT Sep 8, 2020, 7:14 PM

#

@paper echo :white_check_mark: Your eval job has completed with return code 0.

001 | <class 'function'>
002 | <class 'method'>

boreal umbra Sep 8, 2020, 7:32 PM

#

hasattr also lets you use strings, and you can't use variables with the dot operator

#

So it opens up a lot of functionality that's cleaner to write than having lots of try-catch AttributeError

spark venture Sep 8, 2020, 8:38 PM

#

What exactly is Ellipsis/... in Python?

swift imp Sep 8, 2020, 8:57 PM

#

its a shortcut for slicing

#

say you had an 10 dimensional ndarray called x if you wanted to slice say 2,5,10 and everything inbetween 5 and 10 instead of doing x[2,5,6,7,8,9,10] you could do x[2,5,...,10]

#

or something like that, I don't fully understand it myself but its for slicing high dimensional stuff

spice pecan Sep 8, 2020, 9:00 PM

#

numpy arrays use it as a filler for multidimensional slices, yeah

#

IIRC the only use it has in the stdlib are a couple of (relatively) recent cases in typing

paper echo Sep 8, 2020, 9:12 PM

#

wait... what

#

i actually didnt know you could slice a numpy array with ellipses

#

that's also a 3rd party library co-opting it

#

as i understand it, the ellipsis is just a no-op expression

spice pecan Sep 8, 2020, 9:13 PM

#

It's a mystery, really

paper echo Sep 8, 2020, 9:14 PM

#

i wonder when it was added

spice pecan Sep 8, 2020, 9:14 PM

#

It has existed long before the ... literal apparently, and I don't really see how that would be useful?

paper echo Sep 8, 2020, 9:14 PM

#

really?

#

Ellipsis existed before ...?

spice pecan Sep 8, 2020, 9:14 PM

#

yeah, we found that out one of the last times Ellipsis came up in this channel

paper echo Sep 8, 2020, 9:15 PM

#

!e ```python
x = list('abc')
print(x[...])

fallen slateBOT Sep 8, 2020, 9:15 PM

#

@paper echo :x: Your eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "<string>", line 2, in <module>
003 | TypeError: list indices must be integers or slices, not ellipsis

paper echo Sep 8, 2020, 9:16 PM

#

i dont think Ellipsis itself is used anywhere in the CPython source

peak spoke Sep 8, 2020, 9:16 PM

#

It's a nice placeholder for code in stubs or when you're planning to implement something, apart from that I think only typing uses it

paper echo Sep 8, 2020, 9:16 PM

#

maybe ... is

spice pecan Sep 8, 2020, 9:16 PM

#

The stdlib doesn't support Ellipsis anywhere outside of typing

paper echo Sep 8, 2020, 9:16 PM

#

yeah but ... and Ellipsis pre-date those uses @peak spoke e.g. with Protocol

spice pecan Sep 8, 2020, 9:16 PM

#

https://discordapp.com/channels/267624335836053506/709904092280914030/731627131779547298

paper echo Sep 8, 2020, 9:16 PM

#

is it like @/__matmul__ where it was added just for 3rd party libs to use?

spice pecan Sep 8, 2020, 9:17 PM

#

Pretty much, yeah

paper echo Sep 8, 2020, 9:17 PM

#

https://github.com/python/cpython/blob/522691c46e2ae51faaad5bbbce7d959dd61770df/Objects/sliceobject.c#L6-L7 lol

GitHub

python/cpython

The Python programming language. Contribute to python/cpython development by creating an account on GitHub.

#

!e ```python
print(dir(Ellipsis))

fallen slateBOT Sep 8, 2020, 9:17 PM

#

@paper echo :white_check_mark: Your eval job has completed with return code 0.

['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']

spice pecan Sep 8, 2020, 9:17 PM

#

https://docs.python.org/3/library/constants.html#Ellipsis

#

oh wait

#

that's not the right page

#

https://docs.python.org/3/library/stdtypes.html?highlight=ellipsis#the-ellipsis-object

peak spoke Sep 8, 2020, 9:19 PM

#

Don't think there's much to be found about it when the commit that added the object is from 96

spice pecan Sep 8, 2020, 9:19 PM

#

PSF Mysteries Unsolved

peak spoke Sep 8, 2020, 9:29 PM

#

Looks like it was added in 1.4, there's a comment with 11-Oct-1996 GvR renamed Py_Ellipses to Py_Ellipsis :-( in a modsupport.h file but not really sure what that refers to (probably something during development as 1.3 doesn't have either of them in the source)

paper echo Sep 8, 2020, 9:45 PM

#

python is kind of a weird language

#

fascinating development history

#

i loved this talk https://www.youtube.com/watch?v=qCGofLIzX6g

YouTube

Василий Айтипиплов

How Python was Shaped by leaky Internals, Armin Ronacher, Flask fra...

▶ Play video

peak spoke Sep 8, 2020, 9:47 PM

#

the PEPs and issue tracker are fairly easy to go through for features etc. but there's not much to be found for python 1

red solar Sep 8, 2020, 9:59 PM

#

it's always fun looking through the git repository back in early 2000 though (or whenever they put it on github)

paper echo Sep 8, 2020, 10:00 PM

#

there are git commits going back into the 90s

#

github has the whole commit history

#

or a lot of it

peak spoke Sep 8, 2020, 10:07 PM

#

https://github.com/python/cpython/commit/85a5fbbdfea617f6cc8fae82c9e8c2b5c424436d seems to be the first

unkempt rock Sep 8, 2020, 10:29 PM

#

how can i make like "wait for some event" in python... ?
do i need to use async and await ?
or what..?

radiant fulcrum Sep 8, 2020, 10:32 PM

#

@paper echo Thanks for that Talk :P Probably wouldnt have found it without it but damn thats pretty nice

paper echo Sep 8, 2020, 10:32 PM

#

Classes are really hacked in at the last moment.
It should be possible to use other object types as base classes,
but currently it isn't. We'll see if we can fix that later, sigh...
lol

radiant fulcrum Sep 8, 2020, 10:36 PM

#

So ive learn this from the talk: Kill Pickle, Fix imports

sacred yew Sep 8, 2020, 10:55 PM

#

wait whats wrong with pickle

gritty pebble Sep 8, 2020, 11:11 PM

#

Arbitrary code execution stuff

spark magnet Sep 8, 2020, 11:13 PM

#

@sacred yew https://nedbatchelder.com/blog/202006/pickles_nine_flaws.html

Pickle’s nine flaws

narrow kettle Sep 8, 2020, 11:19 PM

#

hmm, i suppose pickle can serialize callables

#

id never reallly thought about that, thats intriguing

spark magnet Sep 8, 2020, 11:22 PM

#

no, it doesn't pickle code

#

but it will run whatever code you tell it to that it can find in the process.

unkempt rock Sep 9, 2020, 12:26 AM

#

I never read an explanation of how pickle is insecure, just knew that it was.

#

Typically I will deconstruct properties fromk objects and put them into json. Then the program that loads the json, will construct objects again using that data. There are situations where that isnt realistic I think, but I do that pretty often.

solar delta Sep 9, 2020, 1:42 AM

#

Right ^ state in methods/classes is a bad idea but for 3rd party objects pickles r fine

#

note; some modules don't work well with pickle; like XGBoost doesn't return the same object you stored

spark magnet Sep 9, 2020, 2:01 AM

#

@solar delta what do you mean, "not the same object"?

#

it's in a new process, isnt it? so it can't literally be the same object

solar delta Sep 9, 2020, 3:02 AM

#

if you pickle an XGBoost model that has been trained the results won't come out the same if you have the same seed.

#

It works fine with Gradient boosting from sklearn though..

leaden sphinx Sep 9, 2020, 4:40 AM

#

Can I post a slightly more advanced question here?

sacred yew Sep 9, 2020, 4:44 AM

#

sure

#

as long as it fits channel topic

charred wagon Sep 9, 2020, 5:09 AM

#

@leaden sphinx There are dedicated channels for Python help. In fact, it's our entire help system #❓｜how-to-get-help. Your question could also go in a topical channel, specifically #databases. This channel is not appropriate because it is a discussion channel, not a help channel.

leaden sphinx Sep 9, 2020, 5:23 AM

#

Thanks

red solar Sep 9, 2020, 5:28 AM

#

In fairness to pickle, it is noted that you should only use it on trusted data

unkempt rock Sep 9, 2020, 6:27 AM

#

k

misty tiger Sep 9, 2020, 6:42 AM

#

why does asyncio's loop.run_in_executor leave a thread open permanently and prevent the program from ever exiting?

example: https://paste.pythondiscord.com/afuqurobuy.py

misty tiger Sep 9, 2020, 7:04 AM

#

continued in #async-and-concurrency

undone hare Sep 9, 2020, 7:30 AM

#

I’m looking at the first CPython commits, that’s pretty interesting https://github.com/python/cpython/commits/master?after=3ff6975e2c0af0399467f234b2e307cc76efcfa9+108000

GitHub

python/cpython

The Python programming language. Contribute to python/cpython development by creating an account on GitHub.

#

It seems like GvR commited python libraries before all the C code

grave jolt Sep 9, 2020, 1:59 PM

#

class CheckAppearance() = LabelAppearance():

class BaseButton() = NoReactivity(), LabelAppearance(), Define():

I'm glad we have different inheritance syntax...

true hollow Sep 9, 2020, 2:03 PM

#

me too

brave badger Sep 9, 2020, 2:04 PM

#

class Foo is a BaseClass1 and a BaseClass2 and a BaseClass3:

#

I jest

true hollow Sep 9, 2020, 2:05 PM

#

are we writing cursed code at this point pithink

pliant tusk Sep 9, 2020, 2:05 PM

#

i wonder if py class Foo(Base1 and Base2): could be hacked together using metaclasses

brave badger Sep 9, 2020, 2:06 PM

#

You'd probably have to mess with the mro

pliant tusk Sep 9, 2020, 2:07 PM

#

basically make and return a new class that has both Base1 and Base2 in its mro

#

dont know if thats possible tho

peak spoke Sep 9, 2020, 2:08 PM

#

Don't think you can, since the and will evaluate them separately

pliant tusk Sep 9, 2020, 2:08 PM

#

could use inspect to get the context and do it that way

#

on __bool__ call

brazen jacinth Sep 9, 2020, 2:11 PM

#

python programmers often ask themselves if they can, not enough times if they should GWmemetownOMEGALUL

pliant tusk Sep 9, 2020, 2:11 PM

#

oh 100%

languid dagger Sep 9, 2020, 2:17 PM

#

You can't override for and but you could use + instead. However is there a reason to since Foo would already be that new class with Base1 andBase2 in the mro

pliant tusk Sep 9, 2020, 2:17 PM

#

see the reason is why not

paper echo Sep 9, 2020, 2:17 PM

#

could use &

pliant tusk Sep 9, 2020, 2:18 PM

#

see but now i really want to try and use and

spice pecan Sep 9, 2020, 2:29 PM

#

& can work, and is not overloadable, it just returns one of the operands depending on their truth values, short-circuiting if the first one is False

#

Although I guess you could hack something together with some inspect magic

half wolf Sep 9, 2020, 2:36 PM

#

You could let the first class trickle through, then go another pass by just reading the AST and redeclare the class as if and worked like that probably

#

Not sure where you'd hook that second pass in.

spice pecan Sep 9, 2020, 2:37 PM

#

I guess you could put that in a decorator or a metaclass/parent class

#

So you'd hook in on __init_subclass__, for example, use some magic to get the declaration line and manually parse the parent list

wide shuttle Sep 9, 2020, 2:56 PM

#

At that point, can you still modify the MRO?

#

My guess is that it's already read-only at that point

spice pecan Sep 9, 2020, 2:57 PM

#

That's true

#

You could do something really dirty I guess

undone hare Sep 9, 2020, 2:58 PM

#

The MRO isn't writable? lemon_thinking

#

I don't see why it would tbh

peak spoke Sep 9, 2020, 3:01 PM

#

You can modify __bases__ at any point with a few hacks

wide shuttle Sep 9, 2020, 3:06 PM

#

Also for a class that does not have other bases than object?

spice pecan Sep 9, 2020, 3:07 PM

#

from inspect import getsource


class Base: pass
class OtherBase: pass


class A(Base and OtherBase):
    pass
        

text = getsource(A).split('\n')
text[0] = text[0].replace(' and ', ', ')
exec('\n'.join(text))

print(A.__mro__)

That's the dirtiest thing I've done in a while

#

PS C:\Users\FarmArt.DESKTOP\Desktop> py test.py
(<class '__main__.A'>, <class '__main__.Base'>, <class '__main__.OtherBase'>, <class 'object'>)```

undone hare Sep 9, 2020, 3:11 PM

#

Wait, that is valid python code? lemon_thinking

#

What is the MRO if you keep the and?

peak spoke Sep 9, 2020, 3:12 PM

#

It evaluates the bool values of the class values and returns the last evaluated as usual

undone hare Sep 9, 2020, 3:13 PM

#

Oh right

boreal umbra Sep 9, 2020, 3:16 PM

#

@peak spoke that happens for and?

#

!e print(2 and 3)

fallen slateBOT Sep 9, 2020, 3:16 PM

#

@boreal umbra :white_check_mark: Your eval job has completed with return code 0.

boreal umbra Sep 9, 2020, 3:16 PM

#

Omg

#

I feel like that's less useful or intuitive as or

spice pecan Sep 9, 2020, 3:17 PM

#

They follow the same logic

boreal umbra Sep 9, 2020, 3:17 PM

#

Right

spice pecan Sep 9, 2020, 3:17 PM

#

Return the left operand if it's enough to determine the truthiness of the entire expression, else the right operand

#

For or, it's enough if the left one is True, but not enough if it's False

#

For and it's the other way round

boreal umbra Sep 9, 2020, 3:18 PM

#

I figured

#

or has some handy uses though

spice pecan Sep 9, 2020, 3:18 PM

#

People used that before the ternary became a thing iirc

#

condition and a or b

undone hare Sep 9, 2020, 3:18 PM

#

I believe it is for optimization reasons at first, and then made into a feature, binary comparisons returns the last compared value

boreal umbra Sep 9, 2020, 3:19 PM

#

I can't think of any obvious uses for this functionality of and

peak spoke Sep 9, 2020, 3:19 PM

#

I've used it a few times

spice pecan Sep 9, 2020, 3:19 PM

#

I don't think I've used that in serious code, but you can do some fun stuff with it

boreal umbra Sep 9, 2020, 3:20 PM

#

def func(thing, a=None):
    a = a or []
    a.append(thing)
    return a

#

Not a perfect example

spice pecan Sep 9, 2020, 3:20 PM

#

The chained comparisons are internally joined by and, so you can abuse that to hack in "custom" operators

grand crag Sep 9, 2020, 3:21 PM

#

Not a perfect example
the thing is that you must compare the types, in addition to comparing the values

spice pecan Sep 9, 2020, 3:21 PM

#

https://discordapp.com/channels/267624335836053506/709904092280914030/746752822715875461

peak spoke Sep 9, 2020, 3:23 PM

#

For example here https://github.com/Numerlor/bot/blob/truncate-internal-eval/bot/utils/services.py#L22 for a use, or and and not returning bools but the last value they evaluated doesn't change much logic (and where it does they can be wrapped in a bool call), but does come in handy at times

spice pecan Sep 9, 2020, 3:24 PM

#

#esoteric-python should have some obscure examples as well

paper echo Sep 9, 2020, 3:44 PM

#

https://mypy-play.net/?mypy=latest&python=3.8&flags=show-error-context&gist=0dfe390f4f5a111429efffb7b83a94e3 is there something wrong with the reduce signature annotation? or is there something wrong with me?

hollow pewter Sep 9, 2020, 3:45 PM

#

Is there any cmd in python to find biggest substring in alphabetical order.

#

GWchadMEGATHINK

#

Or do I need to search it through index?

visual shadow Sep 9, 2020, 3:45 PM

#

Wrong channel. Try #python-discussion. Also sounds like a max should work for you

hollow pewter Sep 9, 2020, 3:46 PM

#

👍

spice pecan Sep 9, 2020, 3:49 PM

#

Actually

#

I was toying around with metaclasses, and now I'm wondering if you can unpack a sequence into a class definition

#

Yes, yes you can

#

>>> class A: pass
...
>>> class B: pass
...
>>> class C: pass
...
>>> bases = A, B, C
>>> class Derived(*bases): pass
...
>>> Derived.__mro__
(<class '__main__.Derived'>, <class '__main__.A'>, <class '__main__.B'>, <class '__main__.C'>, <class 'object'>)

plush root Sep 9, 2020, 4:00 PM

#

how to start weather prediction, I mean use of numeric models (numerical methods)?

charred wind Sep 9, 2020, 4:08 PM

#

hi, my name is Erik

#

nice to meet you all

steep turret Sep 9, 2020, 4:09 PM

#

Heyy Guys! Im new here.. Nice to meet you guys

charred wind Sep 9, 2020, 4:10 PM

#

hello, im new here as well

steep turret Sep 9, 2020, 4:13 PM

#

Idk if here's the right place to ask that.. If its not, i'm sorry ...

Someone here worked with uwsgi?

I'm facing some issues here.. :(

Trying to deploy a project with multiple threads and Flask application. But I can't get it to work...

I want the threads that i'm creating only in main process (right now it is beeing replied on every process), and I want flask (and just flask) in multiple processes... Is this possible at all?

paper echo Sep 9, 2020, 4:13 PM

#

@steep turret you should ask in #web-development

steep turret Sep 9, 2020, 4:13 PM

#

@charred wind hi there!

visual shadow Sep 9, 2020, 4:13 PM

#

#web-development might be the right place

#

This room is reserved for discussions about the python language itself. See the room description for more info.

steep turret Sep 9, 2020, 4:13 PM

#

Ohh

#

good.

#

Thank u guys

#

i'm gonna ask that there

boreal umbra Sep 9, 2020, 4:31 PM

#

Welcome @charred wind! #python-discussion is the best place for introductions and such.

#

Or one of the off topic channels if you want to socialize.

charred wind Sep 9, 2020, 4:32 PM

#

thanks!

heady mauve Sep 9, 2020, 5:01 PM

#

imagine writing ray marching code and making a very crude console 3d graphics system

#

is there a way to modify text colors via RGB with the standard console on Windows 10?

grave jolt Sep 9, 2020, 5:22 PM

#

@boreal umbra

def func(thing, a=None):
    a = a or []
    a.append(thing)
    return a

Well, actually, there's a bug --

x = 42
things = []
func(x, things)
print(things) # []

pliant tusk Sep 9, 2020, 5:34 PM

#

Would need to be a if a is not None else []

peak spoke Sep 9, 2020, 5:36 PM

#

is it a bug though? It returns the list that was appended to

final whale Sep 9, 2020, 5:37 PM

#

would invert that condition to avoid having to use not

grave jolt Sep 9, 2020, 5:43 PM

#

@peak spoke But it suddenly behaves differently when you provide an empty list.

normal field Sep 9, 2020, 5:51 PM

#

@grave jolt what are you expecting things to be?

grave jolt Sep 9, 2020, 5:53 PM

#

the function mutates a in all other cases, so it would make sense that it would mutate an empty list as well

normal field Sep 9, 2020, 5:54 PM

#

So a test case like this would work?

x = 42
things = [24]
func(x, things)
print(things) # [24, 42]

cloud crypt Sep 9, 2020, 5:54 PM

#

there’s a "bug" in the code

#

because it does not mutate anything that evaluates to False, not only None

visual shadow Sep 9, 2020, 5:56 PM

#

Ah, exactly the feature I needed. lemon_pika

cloud crypt Sep 9, 2020, 5:57 PM

#

good time to discuss deferred None-aware operators, huh?

#

👀

normal field Sep 9, 2020, 5:57 PM

#

To expand on @nekit's point, an empty list [] is False-y. So, a in your case would be assigned the second empty list which is a different object than an empty list passed in as a. Hence you're not mutating the initial empty list passed in.

cloud crypt Sep 9, 2020, 6:01 PM

#

def append_thing(thing: T, some_list: Optional[List[T]] = None) -> List[T]:
    actual_list: List[T] = some_list ?? []
    actual_list.append(thing)
    return actual_list``` looks kinda neat

grave jolt Sep 9, 2020, 6:08 PM

#

@normal field I know why it works like that. The problem is that it might not be the intention.

#

For example, if the second argument is reserved for some shared cache, it will not work properly when the cache is empty.

past otter Sep 9, 2020, 7:05 PM

#

i wish i knew programming 😭

cloud crypt Sep 9, 2020, 7:17 PM

#

We all went from the ground up, just keep up the hard work and don't give up! lemon_pleased

azure pewter Sep 9, 2020, 7:31 PM

#

ajax

#

ajax

#

ajax ajax ajax

#

hmmm

unkempt rock Sep 9, 2020, 7:39 PM

#

is this a JSON response ?

#

anyone know off the top of their head?

azure pewter Sep 9, 2020, 7:40 PM

#

im not sure but i think no

edgy tulip Sep 9, 2020, 7:57 PM

#

import module as md
obj1 = md
obj1.a =10```
so why do we not use parenthesis for instantiating through a module?
Given : the code in module is implemented such as to use @properties for functions

raven ridge Sep 9, 2020, 8:12 PM

#

I don't understand the question. The only objects being instantiated there are a module object and an int, both of which don't need parentheses to instantiate because the language has special syntax for instantiating objects of those types (the import statement and integer literals, respectively)

pseudo cradle Sep 9, 2020, 8:44 PM

#

Does Python have an exclusive OR operator that is not bitwise? If it doesn't... why not???

#

It doesn't seem to unless I'm missing something (which I may be)

flat gazelle Sep 9, 2020, 8:45 PM

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It is not all that common, and bool(a)^bool(b) is not horrible

pseudo cradle Sep 9, 2020, 8:45 PM

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I guess

stable grail Sep 9, 2020, 9:12 PM

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bool(a) != bool(b) maybe?

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i do like lakmatiols version better though

#

def logical_xor(string_self, string_other):
    return bool(string_self) ^ bool(string_other)

#

@pseudo cradle

pseudo cradle Sep 9, 2020, 9:15 PM

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Yeah, both of those work

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I just don't like them, haha

stable grail Sep 9, 2020, 9:15 PM

#

if you want it to look more fancy then it is, take a look in the operator module

#

!d operator.xor

fallen slateBOT Sep 9, 2020, 9:15 PM

#

`operator.xor`

operator.xor(a, b)``````py
operator.__xor__(a, b)```
Return the bitwise exclusive or of *a* and *b*.

stable grail Sep 9, 2020, 9:16 PM

#

you have to do a bool() on a and b here as well

pseudo cradle Sep 9, 2020, 9:16 PM

#

Yeah

stable grail Sep 9, 2020, 9:16 PM

#

or implement your own __xor__

pseudo cradle Sep 9, 2020, 9:16 PM

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It just seems like it would be something fairly basic that I'm surprised isn't in the language. We have and and or after all, why not xor that behaves the same way?

stable grail Sep 9, 2020, 9:17 PM

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because edge cases are normally never a good enough reason to implement something into the standard library

#

!d numpy.logical_xor

fallen slateBOT Sep 9, 2020, 9:18 PM

#

`numpy.logical_xor`

numpy.logical_xor(x1, x2, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj]) = <ufunc 'logical_xor'>```
Compute the truth value of x1 XOR x2, element-wise.

Parameters  **x1, x2**array\_likeLogical XOR is applied to the elements of *x1* and *x2*. If `x1.shape != x2.shape`, they must be broadcastable to a common shape (which becomes the shape of the output).

**out**ndarray, None, or tuple of ndarray and None, optionalA location into which the result is stored. If provided, it must have a shape that the inputs broadcast to. If not provided or None, a freshly-allocated array is returned. A tuple (possible only as a keyword argument) must have length equal to the number of outputs.

**where**array\_like, optionalThis condition is broadcast over the input. At locations where the condition is True, the *out* array will be set to the ufunc result. Elsewhere, the *out* array will retain its original value. Note that if an uninitialized *out* array is created via the default `out=None`, locations within it where the condition is False will remain uninitialized.... [read more](https://docs.scipy.org/doc/numpy/reference/generated/numpy.logical_xor.html#numpy.logical_xor)

stable grail Sep 9, 2020, 9:18 PM

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there you go @pseudo cradle

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its implemented in numpy

pseudo cradle Sep 9, 2020, 9:19 PM

#

nice

stable grail Sep 9, 2020, 9:19 PM

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you could also implement your own version of this using lambda calculus

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but that would be way overkill

boreal umbra Sep 9, 2020, 9:41 PM

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@grave jolt its not meant to be a great example, the point is just that if one wanted to have an optional argument that filters exactly any falsy object, that pattern would work.

swift imp Sep 9, 2020, 10:30 PM

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There's xor bc xor is another name for equivalence

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A scalar xor is by definition ==

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Scratch that

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I'm thinking xnor which is equivalence

#

I mean look

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a xor b == (a and not b) or (not a and b)

#

But on that note

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~= is logically equivalent to xor

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If the two things are not equal do this

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So there's really no point

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Bitwise xor is nice bc it's useful for sets and it's used for parity

gleaming rover Sep 9, 2020, 10:38 PM

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it's interesting because I just had a reason to use the equivalent yesterday

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my values were already bool so I just used !=

grizzled marlin Sep 9, 2020, 10:52 PM

#

Hi can someone help me with numpy

#

📎 unknown.png

gleaming rover Sep 9, 2020, 11:07 PM

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Hi can someone help me with numpy
@grizzled marlin this is the wrong channel #❓｜how-to-get-help

grizzled marlin Sep 9, 2020, 11:07 PM

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Maybe

#

I was posting in general but I haven't had luck

gleaming rover Sep 9, 2020, 11:07 PM

#

next time for numpy try #data-science-and-ml

#

this is for discussion, not help.

grizzled marlin Sep 9, 2020, 11:07 PM

#

tyty

#

mbmb

safe hedge Sep 10, 2020, 5:46 AM

#

How does inheritance work with dataclasses?

#

Do you need both the base and subclass to be decorated?

brave badger Sep 10, 2020, 5:53 AM

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If you need to generate new methods for the subclass yes

safe hedge Sep 10, 2020, 5:54 AM

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Are you suggesting if the subclass only adds attributes then you wouldn't need to decorate it?

brave badger Sep 10, 2020, 5:54 AM

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https://docs.python.org/3/library/dataclasses.html#inheritance

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You'd still need to decorate the subclass if you're adding __init__ attributes + generating dunder methods

safe hedge Sep 10, 2020, 5:55 AM

#

Yeah I read that, I was just kind of intrigued by what happens if you make a subclass a dataclass but the parent wasn't

#

Like a mixin situation

#

I had this:

class CoerceIntMixin():
    def __post_init__(self):
        for field in dataclasses.fields(self):
            if field.type is int:
                curval = getattr(self, field.name)
                if curval is None:
                    continue
                setattr(self, field.name, int(curval))

And I was using it as the base of some dataclasses but then I realised I didn't make it a dataclass itself

#

And I couldn't work out if I was headed for some weird bugs

sacred vapor Sep 10, 2020, 11:31 AM

#

I want to add L_0.5 loss in my model while training
i have written :: loss = tf.reduce_sum(tf.pow(tf.abs(self.Coef),0.5))
But its giving NaN Error!
How its working perfectly with L1 loss and L2 loss
loss = tf.reduce_sum(tf.square(self.Coef))
loss = tf.reduce_sum(tf.abs(self.Coef))
the above 2 lines are working perfectly, but i want to use L_0.5 loss....How to do that?

magic python Sep 10, 2020, 11:59 AM

#

https://github.com/PyCQA/pylint/issues/3060

why would abstract-class-instantiated ever matter? I don't even understand the error that this is supposed to catch

GitHub

False abstract-class-instantiated with pandas.ExcelWriter · Issue #...

Hello, Steps to reproduce Run pylint on the following code: """Lorem ipsum""" import pandas as pd def demo(): """Dem...

peak spoke Sep 10, 2020, 12:13 PM

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A class with abstract methods will raise when initialized because those methods should be overriden, the warning is probably there so the error is discovered even when your code doesn't take those paths during testing

magic python Sep 10, 2020, 12:21 PM

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@peak spoke would this be something to read to understand better : https://stackoverflow.com/questions/4382945/abstract-methods-in-python ?

Stack Overflow

Abstract methods in Python

I am having trouble in using inheritance with Python. While the concept seems too easy for me in Java yet up till now I have been unable to understand in Python which is surprising to me at least.

I

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i've not seen abstract methods before, have just heard the name

peak spoke Sep 10, 2020, 1:01 PM

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abcs allow you to create interfaces, if you subclass an abc you either get an error when trying to initialize it without the methods implemented or you get the whole interface the abc defines. For example python provides some in the collections.abc for common data structures in python https://docs.python.org/3/library/collections.abc.html

keen anchor Sep 10, 2020, 4:37 PM

#

You have to write an efficient and pluggable API application. Describe how you would choose which framework to use and which framework you think would be best for the job and why.

#

My question is: What's a pluggable API in the first place?

mint forge Sep 10, 2020, 4:40 PM

#

@keen anchor does this help:

REST service. Also, because the platform is pluggable, it means that you can expose any of your custom code as an API call or REST service as well. This means the days of difficult integration, and siloed functionality are over. Welcome to a RESTful development life!

fiery cloud Sep 10, 2020, 4:40 PM

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does they trying to say, writing handler for certain services?

mint forge Sep 10, 2020, 4:45 PM

#

@keen anchorhttps://docs.mendix.com/apidocs-mxsdk/apidocs/pluggable-widgets

Mendix Documentation

Pluggable Widgets API - APIs & SDK | Mendix Documentation

A guide for understanding pluggable widgets.

keen anchor Sep 10, 2020, 4:45 PM

#

thanks

mint forge Sep 10, 2020, 4:45 PM

#

np

proven dirge Sep 10, 2020, 4:54 PM

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Hi there, anyone has experience of pyinstaller?

vague mica Sep 10, 2020, 5:13 PM

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@proven dirge better to ask more specific questions. Someone having experiece with pyinstaller might not know what you are looking for.

unkempt rock Sep 10, 2020, 5:31 PM

#

#include <iostream>
#include <stdio.h>

#define PVAR(x) printf("var" #x " + 1 = %d\n", var##x + 1) 

int main(void) {
    auto [var1, var2, var3] = (int[3]) {1, 2, 3};
    PVAR(1); PVAR(2); PVAR(3);
}

#

Is it possible to implement something like this in python?

#

Only thing that comes to my mind is ast but I've only used it once so I'm not so sure about it

half wolf Sep 10, 2020, 5:54 PM

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@unkempt rock the new debug feature in f strings?

unkempt rock Sep 10, 2020, 5:57 PM

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Ah..

#

Never knew that existed

paper echo Sep 10, 2020, 6:57 PM

#

Is that the {x=} thing @half wolf ?

radiant fulcrum Sep 10, 2020, 7:36 PM

#

What was the alternative people use over MyPy again?

#

dont get me wrong i love MyPy's system but holy fuck is it slow

cloud crypt Sep 10, 2020, 7:51 PM

#

it is kinda stupid sometimes

#

because of static analysis and other things

#

pyre, pyright and pytype

paper echo Sep 10, 2020, 8:03 PM

#

@radiant fulcrum pyre, pyright, pytype

#

pyre is by facebook, pyright is by microsoft, pytype is one of those "google but not actually google" projects

radiant fulcrum Sep 10, 2020, 8:47 PM

#

im curious to know how many people actually use Pycharm's profiling tools

📎 unknown.png

pearl river Sep 10, 2020, 9:13 PM

#

the spreadsheet view is just cProfile with easy sorting

#

but the graph is 👌

sacred tinsel Sep 10, 2020, 9:55 PM

#

I look at the graph sometimes, it's nice

waxen kindle Sep 10, 2020, 9:56 PM

#

Excuse me i have a question friends

#

I am Ozan i am studying master in data science and i enrolled dataquest datacamp udacity courses

#

what should i do as next after finishing

#

for the future issues , NLP , machine learning engineer like this

#

what are your suggestions thanks for everything . Best regards

gleaming rover Sep 10, 2020, 10:02 PM

#

what should i do as next after finishing
@waxen kindle this is for discussion of the language; why not try #career-advice? you might get better help there

waxen kindle Sep 10, 2020, 10:04 PM

#

Oh okey sorry about this someone in data science channel suggested that channel i enrolled as new

gleaming rover Sep 10, 2020, 10:04 PM

#

Oh okey sorry about this someone in data science channel suggested that channel i enrolled as new
@waxen kindle yup we can talk in #data-science-and-ml, I pinged you

unkempt rock Sep 10, 2020, 11:13 PM

#

anyone know how i can play audio from a URL without using vlc because im having problems with vlc. How can i play audio from an audio url without using vlc

boreal umbra Sep 11, 2020, 12:21 AM

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@unkempt rock take a look at #❓｜how-to-get-help; this channel is specifically for discussion

unkempt rock Sep 11, 2020, 1:11 AM

#

okay

boreal umbra Sep 11, 2020, 2:55 AM

#

is random.shuffle O(n)?

peak pollen Sep 11, 2020, 3:05 AM

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I believe so