Accessing module level variables, from within a function in the module [duplicate]

Question

I'd like to be able to do something like this:

#mymodule
var = None

def load():
    var = something()

Other module(s):

#secondmodule
import mymodule
mymodule.load()

#thirdmodule
from mymodule import var
print var #Shouldn't be None

But I don't know how to reference a modules variable from a function defined in the module.

Is this possible? Or am I going to need to put a global declaration in every place I wan't to use this. Or am I going at this completely wrong?

Answer 1

Just change the function definition to:

def load():
    global var # this line has been added to the original code
    var = something()

Global variables are read-only from sibling methods. More accurately unless a variable is specified as global, Python consider it as local, but a read access to a local variable name will reach module-level scope if the name is not present in local scope.

See also use of “global” keyword in python and the doc for more details about the global statement

Answer 2

You seem to mostly have it. You are missing only the fact that "module-level" variables are called global in Python. (They are not truly global, but only global to the module they are declared in, in other words.)

In any function where you modify a global variable (you want to make the name refer to a different object), it must be declared global. So your load() function needs a global var at the beginning. If you are only using the value of a global variable, or if it is a mutable type such as a list and you are modifying it, but not changing the object that the name points to, you needn't declare it global.

The import statement is, as you have discovered, how you can import a module-level variable from one module into another.