Python – anyone have a memoizing decorator that can handle unhashable arguments?

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Here is the example in Alex Martelli Python Cookbook that show how to create a memoize decorator using cPickle for function that take mutable argument (original version) :

import cPickle

class MemoizeMutable:
    def __init__(self, fn):
        self.fn = fn
        self.memo = {}
    def __call__(self, *args, **kwds):
        import cPickle
        str = cPickle.dumps(args, 1)+cPickle.dumps(kwds, 1)
        if not self.memo.has_key(str): 
            print "miss"  # DEBUG INFO
            self.memo[str] = self.fn(*args, **kwds)
        else:
            print "hit"  # DEBUG INFO

        return self.memo[str]

Here is a link.

EDIT: Using the code that you have given and this memoize decorator :

_level = MemoizeMutable(_level)

equirements = {'a': [],
               'b': [],
               'c': ['a'],
               'd': ['a','b'],
               'e': ['c','d'],
               'f': ['e']
                 }

print uses_hierarchy(equirements)

i was able to reproduce this:

miss
miss
hit
miss
miss
hit
miss
hit
hit
hit
miss
hit
{0: ['a', 'b'], 1: ['c', 'd'], 2: ['e'], 3: ['f']}

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