Closures in Python

Question

I\'ve been trying to learn Python, and while I\'m enthusiastic about using closures in Python, I\'ve been having trouble getting some code to work properly:

Answer 1

Get is not global, but local to the surrounding function, that's why the global declaration fails.

If you remove the global, it still fails, because you can't assign to the captured variable name. To work around that, you can use an object as the variable captured by your closures and than just change properties of that object:

class Memo(object):
    pass

def memoize(fn):
    def defaultget(key):
        return (False,)

    memo = Memo()
    memo.get = defaultget

    def vset(key, value):
        oldget = memo.get
        def newget(ky):
            if key==ky: return (True, value)
            return oldget(ky)
        memo.get = newget

    def mfun(*args):
        cache = memo.get(args)
        if cache[0]: return cache[1]

        val = apply(fn, args)
        vset(args, val)
        return val

    return mfun

This way you don't need to assign to the captured variable names but still get what you wanted.