create a list of an objectA inside the objectA

Question

When I’m trying to append() the object itself into a list inside the object, it doesn’t work, I don’t understand why.

class PLayer:

    CLASS_NAME = "player"
    TOTAL_PLAYER_NUMBER = 0
    TOTAL_PLAYER_LIST = []
    PLAYER_ID_INCREMENT = 0

    def __init__(self, name,
                 first_name,
                 birthday,
                 note,
                 player_id=None,
                 total_score=None,
                 tournament_score=None):

        self.PLAYER_ID_INCREMENT += 1
        self.TOTAL_PLAYER_NUMBER += 1
        self.name = name
        self.first_name = first_name
        self.birthday = birthday
        self.player_id = self.PLAYER_ID_INCREMENT
        self.total_score = 0
        self.tournament_score = 0
        self.note = note
        self.TOTAL_PLAYER_LIST.append(self.Player)

So the class Player have a list TOTAL_PLAYER_LIST = [], then inside the __init__ I want to add the player that have been freshly created to the list with the last line self.TOTAL_PLAYER_LIST.append(self.Player) but I get this error

line 25, in __init__
    self.TOTAL_PLAYER_LIST.append(self.Player)
AttributeError: 'PLayer' object has no attribute 'Player'

I don’t understand why. I’ve tried to put and remove self., the parenthesis also () for Player() .

Asked By: Matteo

||

Source

Answer 1

Remove the `.Player` attribute

If you do this, it works fine. Your class doesn’t have any Player attribute. The player you want to add is referenced in the self variable, the instance.

        self.TOTAL_PLAYER_LIST.append(self)

Let’s see a simpler example with debug:

class Player:
    TOTAL_PLAYER_NUMBER = 0
    TOTAL_PLAYER_LIST = []
    PLAYER_ID_INCREMENT = 0

    def __init__(self, name):
        self.PLAYER_ID_INCREMENT += 1
        self.TOTAL_PLAYER_NUMBER += 1
        self.name = name
        self.player_id = self.PLAYER_ID_INCREMENT
        self.TOTAL_PLAYER_LIST.append(self)

    def __repr__(self):
        return f"{self.name}:<{self.player_id}>"

print(Player("Doe"))  # Doe:<1>
print(Player.TOTAL_PLAYER_LIST)  # [Doe:<1>]

Other critical issue with your code

Name your class Player, not PLayer
Class attribute vs Instance attribute

        self.PLAYER_ID_INCREMENT += 1

This won’t change the class attribute PLAYER_ID_INCREMENT, just create an instance attribute of 1:

doe = Player("Doe")
joe = Player("joe")
print(Player.TOTAL_PLAYER_NUMBER)  # 0
print(doe.TOTAL_PLAYER_NUMBER)  # 1
print(joe.TOTAL_PLAYER_NUMBER)  # 1

Fix this with:

    def __init__(self, name):
        Player.PLAYER_ID_INCREMENT += 1
        Player.TOTAL_PLAYER_NUMBER += 1
        ...

doe = Player("Doe")
joe = Player("joe")
print(Player.TOTAL_PLAYER_NUMBER)  # 2
print(doe.TOTAL_PLAYER_NUMBER)  # 2
print(joe.TOTAL_PLAYER_NUMBER)  # 2

This happens because integers are immutable and += will "rebind" the incremented value to a new reference located… in self, the instance namespace, not the class namespace.

A more pythonic way to do that is with metaclasses:

import typing


class CountInstances(type):
    def __init__(cls, name, bases, dict_):
        super().__init__(name, bases, dict_)
        cls.count = 0

    def __call__(cls, *args, **kwargs):
        cls.count += 1
        return super().__call__(*args, **kwargs)


class Player(metaclass=CountInstances):
    total_player_list: typing.Final = []

    def __init__(self, name):
        self.name = name
        self.player_id = self.count
        self.total_player_list.append(self)

    def __repr__(self):
        return f"{self.name}:<{self.player_id}>"


doe = Player("Doe")
joe = Player("Joe")
print(Player.count)  # 2
print(doe.count)  # 2
print(joe.count)  # 2
print(Player.total_player_list)  # [Doe:<1>, Joe:<2>]

More information about metaclasses: What are metaclasses in Python?

Answered By: Dorian Turba

create a list of an objectA inside the objectA

Question:

Answers:

Remove the `.Player` attribute

Other critical issue with your code

create a list of an objectA inside the objectA

Question:

Answers:

Remove the .Player attribute

Other critical issue with your code

Remove the `.Player` attribute