Modifying a variable in Python

Question

I'm creating a Galaga clone with pygame and I am having issues with using a value in one function that was modified in other function. I created a very simple version of the code to try to debug it but I have not had any luck.

import pygame
import time
pygame.init()
clock = pygame.time.Clock()

var1 = 10

def function3(var1):

    var1 = var1 + 2


def function1():
    gameExit = False
    while not gameExit:
        function3(var1)

        print(var1)
        clock.tick(5)
function1()

My question is (based on this simplified version) how do I display the updated value of var1. I would like print(var1) to display 10,12,14,16...

My guess is to use a global declaration but the closest question that I found on stackexchange was this and it didn't seem to work with my scenario.

Please note that I'm aware that this increase of var1 could be done with a while loop but a while loop will not work with my actual code. I would like an answer (or hint) that utilizes this format (as shown above).

Any suggestions would be appreciated. Thanks!

So you want var1=16 but print(var1) to show "10,12,14,16"? Perhaps you want each print to add to what you have already printed? — John3136
– John3136, Commented Nov 24, 2016 at 22:14
return the value of var1 as well in function3. And initialize it in function1. Refraining a downvote because Galaga is great. — Jean-François Fabre
– Jean-François Fabre ♦, Commented Nov 24, 2016 at 22:14
whoever downvoted this, please go back to facebook or something. — MK.
– MK., Commented Nov 24, 2016 at 22:16

Oleksandr Dashkov · Accepted Answer · 2016-11-25 14:55:34Z

1

You should use return in your function:

import pygame
import time
pygame.init()
clock = pygame.time.Clock()

var1 = 10

def function3(v):
    return v + 2


def function1():
    gameExit = False
    while not gameExit:
        var1 = function3(var1)

        print(var1)
        clock.tick(5)

function1(var1)

edited Nov 25, 2016 at 14:55

answered Nov 24, 2016 at 22:14

Oleksandr Dashkov

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2 Comments

newtonjeep Over a year ago

Thanks! I'm thinking of creating a class as @MK. suggested but return could also work.

user5653854 Over a year ago

This really is the "correct" way in Python as modifying global variables ruins modularization.

MK. · Accepted Answer · 2016-11-24 22:15:01Z

0

Here is "correct" way of doing what you want:

var1 = 10

def function3():
    global var1
    var1 = var1 + 2

print var1
function3()
print var1

Your code is modifying local variable var1 which is only defined within your function3. I put word correct in quotes because global variable is (almost) never a good idea. If you need state (variable) shared between multiple functions, you could create a class. Or you could be modern functional and immutable and have the function take a value as argument, modify and return it.

answered Nov 24, 2016 at 22:15

MK.

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1 Comment

newtonjeep Over a year ago

Good to know. Thanks for your quick response! I'll look into creating a class...

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