🔒 I think it's not a typo

[echo cove]

as code is working fine but idk why he wrote that

[craggy cairn]

@echo cove

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[fossil plinth]

i don't see what's wrong?

[deft galleon]

thats a strange way to explain/show how to use property without it being a decorator

[echo cove]

he create a public attribute in the init method but uses private attribute in the getter\

that is an older way

[deft galleon]

but he did set name = property(...)

[fossil plinth]

ah

[deft galleon]

so when calling Person.name it would run the getter function

[fossil plinth]

i wouldn't really recommended doing it this way

[deft galleon]

same

[fossil plinth]

much clearer to use the decorator

[deft galleon]

it is a decorator... just completely laid out

https://realpython.com/python-property/#getting-started-with-pythons-property

[echo cove]

if i called p.name , the init will be valid?

[deft galleon]

yes its still valid

[echo cove]

what if i use decorators...then?

[deft galleon]

you can either use property as a decorator or just a plain property function call. Either way it works

[echo cove]

but in previous code he uses private attr in the init

[deft galleon]

you could do it both ways but that would be complicating yourself

[echo cove]

wait let me show you

[fossil plinth]

it is common to use a private attr

[deft galleon]

One thing to understand is there is no such thing as "private" btw. You can still access the _ attributes without the @property

[echo cove]

yeah

[deft galleon]

!e

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

p = Person("ajay")
print(p._name)

[craggy cairn]

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

ajay

[deft galleon]

ok so what is the problem with this one?

[echo cove]

nothing, it is working...
but in this the private attr is also in the__init__

ok you wrote it

[deft galleon]

Sorry. I meant, what part of that is confusing you?

[echo cove]

you chose p._name to call as you have written self._name...but in the first image in init it is self.name = name
and when he calls with self.name the getter still prints but getter have self._name. how is it possible of having both the __init__ and getter diff values but sa,e result

wait is it being called directly

[deft galleon]

because you have to use a separate attribute for doing the getter and setter since name is a property, you would do the logic for getters and setters differently. hang on a min

I will show a series of codes that will throw errors and I will do my best to explain it

[echo cove]

ty

[deft galleon]

!e

class Person:
  def __init__(self, name):
    self.name = name # This will cause an AttributeError
  @property
  def name(self):
    return self.name

p = Person("satyam")
print(p.name)

[craggy cairn]

:x: Your 3.14 eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "/home/main.py", line 8, in <module>
003 |     p = Person("satyam")
004 |   File "/home/main.py", line 3, in __init__
005 |     self.name = name # This will cause an AttributeError
006 |     ^^^^^^^^^
007 | AttributeError: property 'name' of 'Person' object has no setter

[deft galleon]

The error here says "property 'name' of 'Person' object has no setter"

That should be obvious as the 'name' property is already decorated, it should have a getter and setter. In this case, the getter is already provided as return self.name but it doesn't know or have the logic to "set" a name

!e
If I add the setter, it looks like this:

class Person:
  def __init__(self, name):
    self.name = name
  @property
  def name(self):
    return self.name
  @name.setter
  def name(self, new_name):
    self.name = new_name

p = Person("satyam")
print(p.name)

[craggy cairn]

:x: Your 3.14 eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "/home/main.py", line 11, in <module>
003 |     p = Person("satyam")
004 |   File "/home/main.py", line 3, in __init__
005 |     self.name = name
006 |     ^^^^^^^^^
007 |   File "/home/main.py", line 9, in name
008 |     self.name = new_name
009 |     ^^^^^^^^^
010 |   File "/home/main.py", line 9, in name
... (truncated - too many lines)

Full output: https://paste.pythondiscord.com/GM3PEG36C7GMVYDWZ67FI2MZVM

[deft galleon]

But now, it throws a different error

  File "/home/main.py", line 9, in name
    self.name = new_name
    ^^^^^^^^^
  [Previous line repeated 995 more times]
RecursionError: maximum recursion depth exceeded

Because it kept calling itself name attribute which is another getter which is also called name

So we basically confused it that the getter for name is also name. To break this recursion, we call the "private" attribute something different like _name, as thats not a decorated property that has a getter or setter

!e

class Person:
  def __init__(self, name):
    self._name = name
  @property
  def name(self):
    return self._name
  @name.setter
  def name(self, new_name):
    self._name = new_name

p = Person("satyam")
print(p.name)

[craggy cairn]

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

satyam

[deft galleon]

It doesn't need to be _ as I pointed out earlier. You could use any other attribute name you want

!e

class Person:
  def __init__(self, name):
    self.temp_name = name
  @property
  def name(self):
    return self.temp_name
  @name.setter
  def name(self, new_name):
    self.temp_name = new_name

p = Person("satyam")
print(p.name)

[craggy cairn]

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

satyam

[fossil plinth]

but it is common to add _ to denote the property and the attr refer to the same thing or are closely related

[deft galleon]

right. thats the usual practice and common understanding between devs that when you want something considered as a "private" attribute in a class, you add a _ to it

And then its just as us devs to see and understand that and be like "ah, that attribute was written to be private. We should just respect that design and variable name as it is"

[echo cove]

we need setter too? cant it run without setter

[deft galleon]

you can run without a setter but that would mean you've already set the value as soon as the class is initialized and skips the __init__

!e

class Person:
  @property
  def name(self):
    return "satyam"

p = Person()
print(p.name)
p.name = "Ajay" #Tries to change to Ajay
print(p.name)

But by doing this, you can't edit the name property anymore.

[craggy cairn]

:x: Your 3.14 eval job has completed with return code 1.

001 | satyam
002 | Traceback (most recent call last):
003 |   File "/home/main.py", line 8, in <module>
004 |     p.name = "Ajay" #Tries to change to Ajay
005 |     ^^^^^^
006 | AttributeError: property 'name' of 'Person' object has no setter

[deft galleon]

its the same if you tried in __init__ too

[echo cove]

ok

[deft galleon]

!e

class Person:
  def __init__(self):
    self._name = "satyam"
  @property
  def name(self):
    return self._name

p = Person()
print(p.name)

This works because you're not "setting" any new value. Its all hardcoded. And of course if you edit or set a new name after that, it throws that AttributeError like before

[craggy cairn]

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

satyam

[echo cove]

ok

@deft galleon

this is confusing to me

[deft galleon]

that looks straightforward... hang on. gimme a min

!e

class Person:
  def __init__(self, name):
    self.name = name # 1) This will set the name value into the self.name property as defined in the next line. But because its a property, it needs a setter.
  @property
  def name(self):
    return self._name # 3) This is the last step. Because the value is already called and set in the setter, this self._name DOES have a value and thus is able to give back what the value is to the property.
  @name.setter
  def name(self, value):
    self._name = value # 2) So when this class instantiates, the setter here will place the "name" value into the `self._name`

p = Person("ajay")
print(p.name)

[craggy cairn]

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

ajay

[echo cove]

wdym by

Because the value is already called
in the init or p.name

[deft galleon]

So the flow goes from setting the "ajay" as an argument in the __init__, then because self.name = name triggers the self.name property's setter defined in @name.setter, it will set the value into self._name and then returns it to the property name

I've numbered them in the comments as 1) 2) and 3) for convenience

[echo cove]

yes i read that,...

ok

got it

that was tricky

it worked

thank you @deft galleon

!close

[craggy cairn]

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