Can global variable be passed into Python function?

Gary Herron gary.herron at islandtraining.com
Fri Feb 21 09:41:59 CET 2014


On 02/20/2014 10:37 PM, Sam wrote:
> I need to pass a global variable into a python function. However, the global variable does not seem to be assigned after the function ends. Is it because parameters are not passed by reference? How can I get function parameters to be passed by reference in Python?

Are you passing a value *into* a function, or back *out of* the 
function?  These are two very different things, and your question 
mentions both and seems to confuse them.

You can pass any value into a function through its parameters, whether 
that value comes from a local variable, global variable, or the result 
of some computation. (But consider: it is the value that is being passed 
in -- not the variable that contains that value.) You can't pass values 
back out from a function through assignment to any of the parameters.

The global statement is a way to allow a function to assign to a global 
variable, but this would not be considered "passing" a global into a 
function.  It's just a way to access and assign to a global variable 
from withing a function.

v = 123

def f(...):
    global v  # Now v refers to the global v
    print(v)  # Accesses and prints the global v
    v = 456 # Assigns to the global v.

Gary Herron



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