Python global variable referenced before assigned a value

Question

I recently started to program in python, and I love it so far. I previously programmed in c# and java, which is probably causing my problem. In c#, if you have a public variable, it will change in each method. Sorry for the bad explanation, but it will be easier to visualize the code.

This code is an example of what I want to happen in python in c# form. The code does not actually work because it's only an example.

class Player
{
    public var player; //create the variable
    public var playerRectangle;
    public var playerMovement;

    public Player()
    {
        player = pygame.image.load("player.png"); //set the variables value
        playerRectangle = player.get_rect();

        playerMovement = new int[0,0];
    }

    public void Update()
    {
        for event in pygame.event.get():
            if event.type == pygame.KEYDOWN and event.key == pygame.K_w:
                playerMovement[1] = -2   //use the variables value
            if event.type == pygame.KEYDOWN and event.key == pygame.K_s:
                playerMovement[1] = 2
            if event.type == pygame.KEYDOWN and event.key == pygame.K_a:
                playerMovement[0] = -2
            if event.type == pygame.KEYDOWN and event.key == pygame.K_d:
                playerMovement[0] = 2

            if event.type == pygame.KEYUP and event.key == pygame.K_w:
                playerMovement[1] = 0
            if event.type == pygame.KEYUP and event.key == pygame.K_s:
                playerMovement[1] = 0
            if event.type == pygame.KEYUP and event.key == pygame.K_a:
                playerMovement[0] = 0
            if event.type == pygame.KEYUP and event.key == pygame.K_d:
                playerMovement[0] = 0

        playerRectangle = playerRectangle.move(playerMovement)
    }
}

The actual python code is:

import pygame

class Player:
    player = None #create the variable
    playerRectangle = None
    playerMovement = None

    def __init__():
        global player
        player = pygame.image.load("player.png") #set the variables value
        global playerRectangle
        playerRectangle = player.get_rect()

        global playerMovement
        playerMovement = [0,0]

    def update():
        for event in pygame.event.get():
            if event.type == pygame.KEYDOWN and event.key == pygame.K_w:
                playerMovement[1] = -2 #use the variables !!ERROR!!
            if event.type == pygame.KEYDOWN and event.key == pygame.K_s:
                playerMovement[1] = 2
            if event.type == pygame.KEYDOWN and event.key == pygame.K_a:
                playerMovement[0] = -2
            if event.type == pygame.KEYDOWN and event.key == pygame.K_d:
                playerMovement[0] = 2

            if event.type == pygame.KEYUP and event.key == pygame.K_w:
                playerMovement[1] = 0
            if event.type == pygame.KEYUP and event.key == pygame.K_s:
                playerMovement[1] = 0
            if event.type == pygame.KEYUP and event.key == pygame.K_a:
                playerMovement[0] = 0
            if event.type == pygame.KEYUP and event.key == pygame.K_d:
                playerMovement[0] = 0

        playerRectangle = playerRectangle.move(playerMovement)

    def returnTexture():
        return player

    def returnRectangle():
        return playerRectangle

It says that the variable is referenced before it was given a value, but I gave it a value in the constructor.

score 3 · Accepted Answer · edited May 23 '17 at 11:51

You have forgotten (or have not read) the use of self in your methods.

You need to put self in the method definitions and use self.<attribute> to reference attributes on the instance.

Example:

class Player(object):

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

    def update_name(self, name):
        self.name = name

bob = Player("Bob")
print bob.name  # Bob

bob.update_name("Bob Jones")
print bob.name  # Bob Jones

Note: That the use of self in method definitions of classes in Python is by convention only; you can use whatever name you like but we widely and typically (by convention) use self.

See: Classes

Python global variable referenced before assigned a value

1 Answers1