Changing Global Variables in Python

Question

I want to modify a global variable from a function in Python 2.7

x = 0
def func():
    global x
    x = 2

If I load this code in the interpreter, and then run func(), x remains 0. How do I modify the value of x from within a function?

EDIT: Here's a screenshot of the interpreter and source code. I'm not sure why it works for others and not for me. http://img18.imageshack.us/img18/9567/screenshotfrom201304222.png

This works as-is for me. Are you sure you've called the function? I paste your code in, call func(), and print x. I get 2. — bbayles
– bbayles, Commented Apr 23, 2013 at 2:35
You could try printing all globals() in func() to see if x is included. — user2032433
– user2032433, Commented Apr 23, 2013 at 4:39

pswaminathan · Accepted Answer · 2013-04-24 22:29:05Z

1

This is a very interesting situation. When I ran your code from an interpreter with from mytest import * I encountered the same issue:

>>> from mytest import *
>>> x
0
>>> func()
>>> x
0

However, when I just did import mytest and ran it from there:

>>> import mytest
>>> mytest.x
0
>>> mytest.func()
>>> mytest.x
2

It turned out fine! The reason, I believe, comes from a line in http://docs.python.org/2/reference/simple_stmts.html#the-global-statement:

Names listed in a global statement must not be defined as formal parameters or in a for loop control target, class definition, function definition, or import statement.

Looks like because it is a parameter in your import statement (by importing all), global is having trouble with it. Do you need to import *, or can you simply import the module whole?

edited Apr 24, 2013 at 22:29

answered Apr 23, 2013 at 5:07

pswaminathan

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