Can not increment global variable from function in python

Question

Possible Duplicate:
Using global variables in a function other than the one that created them

I have the following script:

COUNT = 0

def increment():
    COUNT = COUNT+1

increment()

print COUNT

I just want to increment global variable COUNT, but this gives me the following error:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    increment()
  File "test.py", line 4, in increment
    COUNT = COUNT+1
UnboundLocalError: local variable 'COUNT' referenced before assignment

Why is it so?

The use of `global` among beginners is usually a sign of bad design. — Rik Poggi, May 08 '12 at 21:51
without using `global` you can't modify the value of a global variable inside a function, you can only use it's value inside the function. But if you want to assign a new value to it then you've to use the `global` keyword first. — Ashwini Chaudhary, May 08 '12 at 21:53
This should answer your question: http://stackoverflow.com/questions/423379/using-global-variables-in-a-function-other-than-the-one-that-created-them Looks like Python won't change the global value unless you specify that it's what you want to do. — Phil Nicholson, May 08 '12 at 21:46

score 112 · Answer 1 · answered May 08 '12 at 21:44

112

its a global variable so do this :

COUNT = 0

def increment():
    global COUNT
    COUNT = COUNT+1

increment()

print COUNT

Global variables can be accessed without declaring the global but if you are going to change their values the global declaration is required.

answered May 08 '12 at 21:44

cobie

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Thanks for the solution. This one is better as I have tried already using "count += 1" alone but wasn't working. This worked for me. Thanks. – PravinY Aug 16 '17 at 08:17
5

This no longer works. Old solution. – JumpingJacks May 15 '19 at 14:04
saved my 12 hours of work! thanks – Coder Oct 29 '21 at 17:38
This works for me. Thanks – Micah Nov 04 '21 at 20:06

score 30 · Answer 2 · answered May 08 '12 at 21:44

This is because globals don't bleed into the scope of your function. You have to use the global statement to force this for assignment:

>>> COUNT = 0
>>> def increment():
...     global COUNT
...     COUNT += 1
... 
>>> increment()
>>> print(COUNT)
1

Note that using globals is a really bad idea - it makes code hard to read, and hard to use. Instead, return a value from your function and use that to do something. If you need to have data accessible from a range of functions, consider making a class.

It's also worth noting that CAPITALS is generaly reserved for constants, so it's a bad idea to name your variables like this. For normal variables, lowercase_with_underscores is preferred.

Can not increment global variable from function in python

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