global variable inside main function python

Question

I wanted to define a global variable in main, i.e., a variable that can be used by any function I call from the main function.

Is that possible? What'd be a good way to do this?

Thanks!

Answer 1

What you want is not possible*. You can just create a variable in the global namespace:

myglobal = "UGHWTF"

def main():
    global myglobal # prevents creation of a local variable called myglobal
    myglobal = "yu0 = fail it"
    anotherfunc()

def anotherfunc():
    print myglobal

DON'T DO THIS.

The whole point of a function is that it takes parameters. Just add parameters to your functions. If you find that you need to modify a lot of functions, this is an indication that you should collect them up into a class.

* To elaborate on why this isn't possible: variables in python are not declared - they are created when an assignment statement is executed. This means that the following code (derived from code posted by astronautlevel) will break:

def setcake(taste):
    global cake
    cake = taste
def caketaste():
    print cake #Output is whatever taste was

caketaste()

Traceback (most recent call last):
  File "prog.py", line 7, in <module>
    caketaste()
  File "prog.py", line 5, in caketaste
    print cake #Output is whatever taste was
NameError: global name 'cake' is not defined

This happens because when caketaste is called, no assignment to cake has occurred. It will only occur after setcake has been called.

You can see the error here: http://ideone.com/HBRN4y