That python "closure" is a big fat lie too due to python's late binding. Depending on the context in which that code is being defined it may or may not work as expected.

The only guaranteed way to ensure that a free variable in python function scope (it's not a closure) does not change is to pass it explicitly as a default value.

    a = 1
    def function(x, a=a):
        return x + a

That will work in loops. Otherwise what you are really writing is

    a = 1
    def function(x):
        return x + the_last_value_a_obtains_in_this_scope

    a = 2
    assert function(1) == 3