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.
2 Answers
Yes, but why?
def a():
globals()['something'] = 'bob'
8 Comments
Ashwini Chaudhary
just do,
global something, it will create a new global variable if it doesn't exist.
Jon Clements
explicit rather than implicit... - this makes it more "obvious" as to it's a bad idea...
WoooHaaaa
@F3AR3DLEGEND globals my_var does usable outside the function, i've tried that.
ideasman42
While correct, this isn't standard practice. in most cases its best to use
global keyword.
TheTechRobo
it may not be standard practice but it saved me a codefactor headache
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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.
2 Comments
Terrence Brannon
it's not global is it? I think it's module-wide.
Rushy Panchal
Ah yes, it is only module-wide. However, using the
return function should fix that.
global my_var, you're done.