Python Shell cannot run a module with more than one while loop

Question

I have serious problems in being able to build a functional module in which I have to use more than 1 while loop, because the program stops running.

Especially when I use modules like pygame and Tkinter, where my goal is to build a game, but I need to use more than 1 while loop, only if I run it stops working. In this situation I intend to run two while loops at the same time, but the window fails to respond. Why?

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Also I did not understand why my while loop does not cease to exist when I turn the variable 'playing' True? In this situation I just want to run a while loop at a time, the switch off of the while loop is when the 'playing' variable becomes True. Here’s the code:

playing = False
def play():
    playing = True

def gameloop():
    ...
    play()

while not playing:
    gameloop()

while playing:
    gameDisplay.fill(black)
    pygame.display.update()
    clock.tick(15)

The problem is that the second while loop does not run and the first one does not stop running when I call the play() function, even if it declares the global 'playing' variable. Why?

Using python 3.5.0 with Windows 10

I see no reason for windows not responding when I run more than one while loop, because with other people’s pc works perfectly. The problem will be from my pc?

Answer 1

The run that when you put:

def play():
    playing = True

The interpreter created playing as a local variable, so even if you change the value within play the playing global will remain False.

Declaration of the global variable

To tell the interpreter that you want to use the global variable, pass the attribute global for the variable in the method. If the variable does not exist, it is instantiated. Tested in python3.4 (Gentoo Linux)

def play():
    global playing
    playing = True

Contrary to what many beginners think, to use a global variable it is not enough to just declare it at the top of the file, you need to specify in the method that will use a global variable.

If it does not work, it is possible to use alternative methods.

Library

vars.py:

playing = False

main py.:

import vars

...

def play():
    playing = True

...

while not vars.playing:
    ...

This method, imports the variables of a python file, so when it references the variable, it is passed its path so the method does not create a local variable.

Static

def gameloop():
    self.playing = True
gameloop.playing = False

...

while not gameloop.playing:

Dict

conf = {
    'playing' : False,
}

def play():
    conf['playing'] = True

...

while not conf['playing']:
    ...