Posts tagged "hacks"

Closure is truly wonderful. JavaScript — despite its plethora of quirks — is now widely appreciated, thanks in large part to its lexical scoping. Python 3 is lexically-scoped, too, as the following code demonstrates.

def cache(saved=None):
    def _(thing=None):
        nonlocal saved
        if thing is not None:
            saved = thing
        return saved
    return _
cache = cache()

If (the rebound) cache is passed no arguments (or None), saved is returned. Otherwise, thing is assigned to saved and returned.

>>> cache(2**3)
8
>>> cache()
8

This works thanks to the nonlocal keyword introduced in Python 3, which enables variables in outer scopes to be rebound. So how would one achieve the same result in earlier versions of Python?