Share variables between modules

Question

I have this situation:

library_file1.py:

class A:
    def foo(self):
        print("bar")

    def baz(self):
        pass

project_file.py:

from library_file1 import A
class B(A):
    def baz(self):
        print(the_variable)

library_file2.py:

from project_file import B

the_variable = 7
b = B()
b.foo()   # prints "bar"
b.baz()   # I want this to print "7", but I don't know how

How do I allow code to be written in project_file.py that can access variables from library_file2.py? The only solution I can think of is this:

project_file.py:

from library_file1 import A
class B(A):
    def baz(self, the_variable):
        print(the_variable)

library_file2.py:

from project_file import B

the_variable = 7
b = B()
b.foo()
b.baz(the_variable)

but this feels awkward and doesn't scale to many variables like the_variable.

You can use list of variables `b.baz( [var1, var2] )` or dictionary `b.baz( {'var1':7, 'var2':9} )` and then you have to rebuild `baz()` — furas, Jul 02 '14 at 12:39
@furas But then the variables would have to be used as `the_variable[7]` which is quite unclear. I could pass an instance of a custom class, and do `the_variable.var1` which would be better, but I'd still like to avoid that if possible. — rlms, Jul 02 '14 at 12:43

score 1 · Answer 1 · answered Jul 02 '14 at 12:43

Quite easy: you need the variable to be in project_file.py instead of library_file2.py. Change project_file to:

from library_file1 import A
the_variable = None

class B(A):
    def baz(self):
        print(the_variable)

And then in library_file2:

import project_file
from project_file import B

project_file.the_variable = 7
b = B()
b.foo()   # prints "bar"
b.baz()   # prints "7"

Using an argument is also a good solution (you should avoid globals as much as you can).

There is no such a thing as a truly global variable in python. Variables are always attached to a scope. We usually say that a variable is "global" when it's in the module scope.

The widest scope is the built-in scope, so it would be theoretically possible for you to add something as a built-in. However this is a really bad practice. Also it doesn't complete fix the problem, because all files could access that new built-in, but they couldn't re-assign it without explicitly mentioning the scope.

Share variables between modules

1 Answers1