Is it possible to define global variables in a function in Python

Question

How do I declare a global variable in a function in Python?

That is, so that it doesn't have to be declared before but can be used outside of the function.

I think this question should be re-opened because in its current form, it asks a specific Python-related question, and that question has a specific objective answer. — Ron, Oct 16 '18 at 15:30
@TheTechRobo36414519 that's most likely because in most cases it's a bad idea. But if you know why you're doing it then you can silence the error. — Ashwini Chaudhary, Sep 05 '20 at 19:38

score 43 · Accepted Answer · answered Nov 29 '12 at 14:24

43

Yes, but why?

def a():
    globals()['something'] = 'bob'

answered Nov 29 '12 at 14:24

Jon Clements

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just do, `global something`, it will create a new global variable if it doesn't exist. – Ashwini Chaudhary Nov 29 '12 at 14:25
4

explicit rather than implicit... - this makes it more "obvious" as to it's a bad idea... – Jon Clements Nov 29 '12 at 14:26
4

@F3AR3DLEGEND *globals my_var* does usable outside the function, i've tried that. – WoooHaaaa Nov 29 '12 at 14:52
2

While correct, this isn't standard practice. in most cases its best to use `global` keyword. – ideasman42 Jun 12 '14 at 02:54
it may not be standard practice but it saved me a codefactor headache – TheTechRobo the Nerd Sep 06 '20 at 00:00
I believe this is the only way to do it if ``"something"`` variable name is programmatically generated – Azmisov Jan 28 '21 at 02:57
@Azmisov either that or exec – TheTechRobo the Nerd Feb 27 '21 at 22:41
I can think of at least one use-case: I want to mass-produce a bunch of variables in a module (variables whose name would be determined by a set of arguments) and I want to be able to import these variables whenever the module is imported. Is there a cleaner way to do such a thing? – Dec 19 '21 at 12:28

Rushy Panchal · Answer 2 · 2012-11-29T16:35:10.773

def function(arguments):
    global var_name
    var_name = value #must declare global prior to assigning value

This will work in any function, regardless of it is in the same program or not.

Here's another way to use it:

def function():
    num = #code assigning some value to num
    return num

NOTE: Using the return built-in will automatically stop the program (or the function), regardless of whether it is finished or not.

You can use this in a function like this:

if function()==5 #if num==5:
    #other code

This would allow you to use the variable outside of the function. Doesn't necessarily have to be declared global.

In addition, to use a variable from one function to another, you can do something like this:

import primes as p #my own example of a module I made
p.prevPrimes(10) #generates primes up to n
for i in p.primes_dict:
    if p.primes_dict[i]: #dictionary contains only boolean values
        print p.primes_dict[i]

This will allow you to use the variable in another function or program without having use a global variable or the return built-in.

Ah yes, it is only module-wide. However, using the `return` function should fix that. — Rushy Panchal, Nov 29 '12 at 14:39

Is it possible to define global variables in a function in Python

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