How can a function set the value of a variable without returning the value of that variable?

Question

I want to import a particular and unusual module. In order to import this module, I must prepare the environment for its import, import the module, and then change the environment again following its import. The way I can do this is as follows:

argv_tmp = sys.argv
sys.argv = []
from ROOT import *
sys.argv = argv_tmp

I want to abstract the procedures surrounding the actual import into two functions resulting in main code of the following form:

pre_ROOT_import()
from ROOT import *
post_ROOT_import()

How can these functions -- functions that take no arguments and return no values -- perform these procedures?

Answer 1

A context manager works well here. It holds sys.argv locally and restores it even if an exception is raised in ROOT.

import contextlib
@contextlib.contextmanager
def argv_tmp():
    tmp = sys.argv
    sys.argv = []
    try:
        yield
    finally:
        sys.argv = tmp

with argv_tmp():
    from ROOT import *