🔒 Help with classes and lists.

[halcyon beacon]

class Shopcart:
     def __init__(self):
        self.shoplist = [] 

    def insert(self, item):
        self.shoplist.append(item)

    def showlist(self):
         print(self.shoplist)

    def remove(self, item):
         item = input("what do you want to remove?")
             for thing in shop list:
                if item == thing:
        self.shoplist.remove(objet)

shopcart = Shopcart()

shopcart.insert((input("What are you gonna buy?"))
shopcart.showlist()```

[last sand]

@halcyon beacon

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[ionic prawn]

and?

[main cypress]

Hmm why we inserting into shopcart

[amber torrent]

mind your indentations, they need to be correct

[halcyon beacon]

I'm doin it on phone

So it's kind of hard to see them

[halcyon beacon]

This is mostly what I could do from mind without syntax highlighting to see obvious errors, I want to get more into how classes, but specially lists work, because I just have basic understanding of these topics.

[main cypress]

From what I see you have a extra space before everything

[shrewd bough]

the init function is one space too far

[main cypress]

I think

[sharp furnace]

It might make more sense to show the user a selection of items they could possibly buy (either hard-coded or pulled from a file or database or something), validate that selection when they make one, then add it to their cart.

[amber torrent]

i see, but in python the code won't work if it's not correct

so they are essential to get right in python

[halcyon beacon]

Yeah, don't mind the indentation, I can't do it right on phone and don't have access to my PC for now. 😭

Or is there a text editor for this on phone?

Discord just scrambles my text

[main cypress]

Try pyroid ig

It's a python interpreter

Its in playstore

[sharp furnace]

If you're fine with using the browser you could use a site like https://www.online-python.com/

[halcyon beacon]

Tyyy

I usually indent with tab on vs code so I'm kinda lost on my phone 😭

[burnt rover]

what help do you need?

[halcyon beacon]

This

I want to know what else can I do with lists specifically, classes are something secondary for now

Oh, I had a typo, I put remove(object) instead of thing

[main cypress]

Hmm everything about you is interesting

[sharp furnace]

Have you heard of and/or studied list comprehensions?

[shrewd bough]

There are some indentation errors. self.shoplist.remove(objet) what is objet? I think you meant to remove item.
And in the remove function you dont have to insert the argument "item" if you define the variable "item" inside the function

[halcyon beacon]

So instead of remove(self, item), I can just put self?

[burnt rover]

classes and lists are two different things, kinda, lists allows you to dynamically store and remove data from it.

Classes, traditionally are a "template" for creating your custom data type. The data type can do different things. For example, list is also a class, an in built one.

I'd recommend you to explore both of these separately on your own and see how they work

[shrewd bough]

Yeah, because in your case you're asking for item as an input only if you call the function

[halcyon beacon]

Ah, right

[halcyon beacon]

Then, let's get rid of classes and go on with lists since it's the simpler topic.

For example, if I have a list, I know I can put stuff in and out with append and remove

[burnt rover]

Sure, you can do this with just normal functions and list operations, you aren't really making use of OOP here tbf

[halcyon beacon]

I know there are different types of lists

dictionaries, tuples and sets, what's the difference?

[shrewd bough]

Are you doing this project to learn about classes or learm about lists?

[halcyon beacon]

Kind of both, but we'll start with lists

[sharp furnace]

Do you know how to filter elements out of that list easily? Say you want to find all items that start with a certain letter (assuming all items in the list are strings). Would you know how to do that?

[halcyon beacon]

Then I'll go on to classes

[halcyon beacon]

Mhmm

Let me see

[shrewd bough]

I'd say the same thing. Start with lists first then move to classes

[amber torrent]

if we should nitpick here, list are a class, just like all data types in python
but i understand what you mean to say here in this context

[halcyon beacon]

Lets say I have a list with

["Apple", "Soda", "Water", "Milk", "Pineapple", "Almond Milk"]

and I want just the items that start with "A"?

Wasn't that something like .startswith("a")

[amber torrent]

those aren't different types of lists, they are completely different data types, different types of collections, but all of them being collections they share some traits with each other

[shrewd bough]

Yeah you can use startswith or check at the 0th index

[proven sail]

Unless the string is empty

[halcyon beacon]

Ok ok ok

[shrewd bough]

ik but in for loop it would just pass

[sharp furnace]

Yes, and you can create a new list of just those elements using a list comprehension:

some_lst = ["Apple", "Soda", "Water", "Milk", "Pineapple", "Almond Milk"]

print([item for item in some_lst if item.startswith("A")])

[burnt rover]

They are different types of data structures which are built in for you.

Each of them have their own ways of storing data, with their pros and cons, and you need to choose the best one depending on the scenario.

lists: It's a variable length data structure that allows you to add, remove, index through elements in it.

tuples: This is an immutable data structure, best for when you have some constant data that you don't want to change

dictionary: Stores data in a key-value format, you can assign a "key" which can be a string, integer, float, bool, etc (an immutable datatype) which will represent a value.

set: This is an unordered data type and only holds unique values. If you don't care about in which order your data is present or only want to keep track of unique data, it's the best

[burnt rover]

Yeah, I did mention lists are a class as example there lol

[halcyon beacon]

Oh, I was making it. It ended up being larger than yours.

things = ["Apple", "Soda", "Water", "Milk", "Pineapple", "Almond Milk"] 
for item in things:
    if item.startswith("A"):
        things.remove(item)
        
print(things)

Is it right?

[proven sail]

This does not work

!e

things = ["Apple", "Almond Milk"] 
for item in things:
    if item.startswith("A"):
        things.remove(item)
        
print(things)

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

['Almond Milk']

[amber torrent]

you shouldn't modify a collection that you are iterating through, that will just cause a lot of headache

[halcyon beacon]

Ok, ok, so let's set classes even farther away, I need to understand those too. :b

[halcyon beacon]

Which would be the best way to do this?

[burnt rover]

If you find yourself having to mutate a list in a loop, the best way to go about it would to have another list containing the elements you want or not (whichever you need), instead of mutating the original list

[amber torrent]

to create a new list and put everything in that you want to keep is one way, list comprehension more or less does that in one line

[halcyon beacon]

So I have to make a second list that's empty and append the items I want in that list?

[sharp furnace]

Nope. Take a look at my code that uses a list comprehension again: #1483153472172855366 message

[amber torrent]

that or make a list comprehension that does more or less that without you needing to create the empty list first

[halcyon beacon]

things = ["Apple", "Soda", "Water", "Milk", "Pineapple", "Almond Milk"] 
final = []
for item in things:
    if item.startswith("A"):
        final.append(item)
        
        
print(final)

[proven sail]

You can also iterate in reverse

if just removing

[amber torrent]

you now you can run code here, right?

[halcyon beacon]

That looks way more confusing uhh

[proven sail]

and if you're modifying the index while maintaining the same size, then it's fine to mutate

[halcyon beacon]

So you can put the functions inside [] and it'll be a list itself?

[proven sail]

No what

[halcyon beacon]

I mean what he did

[proven sail]

you can rewrite the for loop as a list comp yes

[halcyon beacon]

[items for item in somelist if item.startswith("A")]

it creates a list with what the code specified inside it?

[burnt rover]

they are calling the function inside the list comprehension, you can call a function anywhere, what matters is what the function is returning into the for loop of it

[burnt rover]

yes

and it should be [items for item in somelist if item.startswith("A")]

[halcyon beacon]

That's really useful, ty Peachteaenjoyer :3

[sharp furnace]

Basically yeah, a new list. It's saying for every item in the existing list where if item.startswith("A") is true, give me all of those items in a new list

[halcyon beacon]

Ok, so

If I want to print a list, it's printed as the list itself, that's ugly

What if I want

Apple, Soda, Almond Milk, etc

[burnt rover]

you can assign the list comprehension to another variable and for loop over it again and print it however you want

[sharp furnace]

No prob 🙂

[halcyon beacon]

so

for items in somelist:
    print(item)

[burnt rover]

Or use some useful string functions to do it for you

[burnt rover]

It will print every item in a new line, if that's what you want

[halcyon beacon]

And how do I make it a single line?

[burnt rover]

I can show you two ways

[halcyon beacon]

Let me see, let me see

[sharp furnace]

print(*somelist, sep=", ")

[burnt rover]

Do you know about the end argument in the print function?

Or you could do that too

Would be better

Or if you wanna do with string method,

print(", ".join(somelist))

[halcyon beacon]

I saw it on the CS50 thing but I don't remember anymore

[halcyon beacon]

why the *?

[burnt rover]

!e

fruits = ["Apple", "Banana", "Orange"]
formatted = ", ".join(fruits)
print(formatted)

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

Apple, Banana, Orange

[sharp furnace]

Unpacks the elements of the list so it doesn't have those quotes around all the strings

[halcyon beacon]

OHHHHHH

That's kinda cool

[burnt rover]

In formatted = ", ".join(fruits)

", " is the separator for all elements
And inisde the .join() you pass in an iterable data that you want to have the separator applied on

[halcyon beacon]

Ok, ok

Interesting methods of doing this

[halcyon beacon]

Oh wait, I have an idea

!e

fruits = ["Apple", "Banana", "Orange"]
print(", ".join(fruits))

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

Apple, Banana, Orange

[halcyon beacon]

OOHH IT WORKS

[burnt rover]

Indeed

I just put the extra variable to make it easier to read, you can still print it directly if you wish to

[halcyon beacon]

Then I chan change the separator to any str?

!e

fruits = ["Apple", "Banana", "Orange"]
formatted = "and ".join(fruits)
print(formatted)

[burnt rover]

Just remember that string is an immutable data type, none of the string methods mutate the data within it, it always returns a new string, so don't forget to either store the data in a new variable or print it out

[halcyon beacon]

Immutable and mutable is kind of confusing for me, but what I get is:

Immutable can't be changed after.

Mutable can?

[burnt rover]

Yes, you'll need to fix the formatting

[halcyon beacon]

!e

fruits = ["Apple", "Banana", "Orange"]
formatted = " and ".join(fruits)
print(formatted)

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

Apple and Banana and Orange

[halcyon beacon]

Niceeee

[burnt rover]

Mutable means the data can be changes "in place", i.e a new object isn't created while the data is being changed.

Immutable means the data cannot change "in place", if you want to make some changes to an immutable data, a new object is created.

I'll give an example

!e

fruits = ["apple"]
print(f"{id(fruits)=} | {fruits=}")
fruits.append("banana")
print(f"{id(fruits)=} | {fruits=}")

print()

fruit_string = "orange"
print(f"{id(fruit_string)=} | {fruit_string=}")
fruit_string += ", cherry"
print(f"{id(fruit_string)=} | {fruit_string=}")

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

001 | id(fruits)=140373599426688 | fruits=['apple']
002 | id(fruits)=140373599426688 | fruits=['apple', 'banana']
003 | 
004 | id(fruit_string)=140373597628928 | fruit_string='orange'
005 | id(fruit_string)=140373597860784 | fruit_string='orange, cherry'

[burnt rover]

I used the id function which returns the object's memery address. For the list example at the top, when i mutated it, the memory address remains the same before and after it was mutated, as it's a mutable data type. No new object was created when it did so

But for a string, when i tried mutating it, an entirely new object was created when doing so, hence the memory address is different. String is an immutable data type

@halcyon beacon you understand?

[halcyon beacon]

uhhhh

[halcyon beacon]

Ohhhhhhhh

That's an incredibly cool explanation. Ty.

[burnt rover]

No problemo

[halcyon beacon]

I had to go wash the dishes and now I have some other chores to do, but I want to keep this conversation for when I come back, it's being really useful

[burnt rover]

Alright, I'll still be on for while

[halcyon beacon]

Came back asap.
Ok, ok, so now, what else can I do with lists outside of

append, remove, startswith?

[amber torrent]

!e - did you see that you could do it like this too?

fruits = ["Apple", "Banana", "Orange"]
print(*fruits, sep=" and ")

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

Apple and Banana and Orange

[burnt rover]

startswith is a string method, not list

Lists are mainly designed for adding and removing elements during runtime. That's about it

[halcyon beacon]

Oh, so what about dictionaries? The keys and values you mentioned

[halcyon beacon]

Oh, yes, Peach guy told me about this way too

[burnt rover]

!e

player_data = {
    "name": "Saber",
    "coins": 900,
    "high_score": 10
}

print(player_data["name"])
print(player_data["coins"])
print(player_data["high_score"])

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

001 | Saber
002 | 900
003 | 10

[burnt rover]

Over here, name is a key representing the value "Saber", coins representing 900 and high_score representing the value 10

You can access the values of the keys by this syntax: dict_name[key_name] which will return the value associated with the key_name

You can update, add and remove data from the dict in a similar way too

!e

player_data = {
    "name": "Saber",
    "coins": 900,
    "high_score": 10
}

# Adding a new entry
player_data["current_score"] = 0

# Updating an existing entry
player_data["name"] = "Jiggly"

# Removing an entry
del player_data["coins"]

print(player_data)

[last sand]

:white_check_mark: Your 3.14 eval job has completed with return code 0.

{'name': 'Jiggly', 'high_score': 10, 'current_score': 0}

[burnt rover]

Also the keys need to be of immutable data types only, such as integers, floats, strings, bools, tuples and such

[amber torrent]

frozenset is also fine to use and comes in handy sometimes

[last sand]

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