Python how to pass class function from instance to another class

Question

I have a class of Player with a number of attributes to measure their overall state. I have a second class of Character (Class Type) that sets up some unique configurations for my players depending on their instance of character. Where I am having trouble, is calling a single generic function at the player level that measures the unique milestone goals for each character. i.e Check each player to see if they have reached their unique Milestone 1. I originally tried to do this with a series of conditional functions under the initialization, but this proved to be ill-advised in a class, so I moved it out to its own single function. Since doing this, it obviously fails because the attributes the function are checking for are in the parent class (Player) and not the class where the function is defined (Character).

class Player:
    def __init__(self, player_num, name):
        self.character = Character(name)
        self.player_num = player_num
        self.name = name
        self.power = 0
        self.position = 1
        self.attributeLimit = 4
        self.attributes = []
        self.attachments = []
        self.collection = []
        self.visited = []
        self.setCharacterValues()
        self.ms1 = self.character.Milestone1 

        def setCharacterValues()
        #Loads Character instance data into the Player instance.

class Character:
    def __init__(self, name):
        self.attributes = []
        self.attachments = []
        self.collection = []
        self.visited = []
        self.name = name
        if name == 'char x':
            self.attributes = [1,2,3]
            #etc.
        #etc.

    def Milestone1(self):
        if self.name == 'char x':
            if self.power >= 20:
                return True
            else:
                return False
        if self.name == 'char y':
            if self.position >= 5:
                return True
            else:
                return False
        #etc

for i in players:
    if i.ms1():
        print('Passed')

Now the only solution that I can think of, is to simply move the function from the Character class to the Player class. But this seems to be counter intuitive to me, because this function is measuring each unique characters ability to reach the milestone. It feels appropriate to leave it under Character, and I'm just missing an obvious step somewhere. Can anyone lend some assistance?

Why don't you use inheritance instead?

Henry Yik
– Henry Yik

2019-08-29 03:39:34 +00:00
Commented Aug 29, 2019 at 3:39 — Henry Yik
– Henry Yik, Commented Aug 29, 2019 at 3:39
It was solved using SubClass / Inheritance. Thank you!

Drew Aschenbrener
– Drew Aschenbrener

2019-08-30 01:38:01 +00:00
Commented Aug 30, 2019 at 1:38 — Drew Aschenbrener
– Drew Aschenbrener, Commented Aug 30, 2019 at 1:38

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

Please post the traceback error messages. I think the problem is in Milestone1() you check self.power and self.position but self refers to the instance of Character not Player, and character has no power or position attributes.

Here are 2 fixes I can think of:

Inheritance: If you make player a subclass of character, then player would have all of the attributes of character and therefore be able to call ms1()
```
class Player(Character):
    def __init__(self, player_num, name):
        # self.character = Character(name)  <-- not needed
        # self.ms1 = self.character.Milestone1  <-- not needed

        # since Player is a subclass of Character,
        # use super to init & it already has name and Milestone1
        super().__init__(name)  # Py3 usage
        # super(Player, self).__init__(name)  # Py2 usage
```
I tested this out in a simple example on repl.it and it works for me, try it by pressing play, output is 'n', then 't'.

Note: in Python-2, the syntax for super is different than Python-3, and you must also supply the subclass, Player, and the instance, self as args. I tested inheritance with super(Player, self).__init__(name) in this sample repl.it using Python-2 and it also works.

Also Note: Python-2 classes should subclass object to create new-style classes.

Composition:Fix Milestone1() so it uses player as an argument, and therefore has access to power and position

class Character:
    # no change

    def Milestone1(self, player):
        if self.name == 'char x':
            if player.power >= 20:
                return True
            else:
                return False

update Player too, passing the player instance to Milestone1

class Player:
    def __init__(self, player_num, name):
        self.character = Character(name)

        # self is the Player, lambda makes ms1 callable
        self.ms1 = lambda: self.character.Milestone1(self)

Although then the name attribute isn't really used, and this seems a bit hacky, but I tested it in this simple repl.it example and it also works.

In general, I think this is a good opportunity to use inheritance over composition. Ask yourself:

Is a player a character? (Inheritance: #1)

Does a player have a character? (Composition: #2)

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 29, 2019 at 4:04

Mark Mikofski

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7 Comments

Drew Aschenbrener Over a year ago

Hi Mark, I'm responding from my phone, but I think Inheritance is exactly the solution I an expecting to solve this. I will review it tonight. Thank you!

Drew Aschenbrener Over a year ago

This seems to work fine on Python3, but running my script in 2.7 I keep getting this error:(TypeError: must be type, not classobj) from the line super().__init__(name)

Mark Mikofski Over a year ago

sorry in Python-2, super is different, you have to call super(subclass, self).__init__(self, x, y, ...)

Mark Mikofski Over a year ago

but in Python-2, you should also subclass all your classes to object, Python-3 fixes that. I assumed you were using Python3 because you didn't use object in your classes, e.g. class Character(object): # do stuff

Mark Mikofski Over a year ago

Note there's a typo in the comment above on super for Python-2. It should say super(subclass, self).__init__(x, y, ...) i.e. no self argument in __init__, just in super - oops!

|

ab123 · Accepted Answer · 2019-08-29 03:22:54Z

0

I'd recommend initizliaing a power value in the Character class as well, or creating a generic method in the Character class and then overriding it in the Player class.

answered Aug 29, 2019 at 3:22

ab123

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Comments

hobs · Accepted Answer · 2019-08-29 03:41:04Z

0

What you have is a container class Player that has a one-to-one relationship with the Character. You do not want to duplicate the attributes of Character (like ms1 within Player, especially not during __init__ before anything at all has happened in your game. Instead just access that Character's attributes from the Player instances whenever you need to check them:

player = Player(player_num=42, name='Ivan')
# do some stuff with `player` and `player.character` as the game progresses
# then somewhere deep in the game...
if player.character.ms1:
    print("Congratulations on achieving your first milestone!")

answered Aug 29, 2019 at 3:41

hobs

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