How to memoize **kwargs?

Question

I haven\'t seen an established way to memoize a function that takes key-word arguments, i.e. something of type

def f(*args, **kwargs)

since

Answer 1

Here:

from functools import wraps

def memoize(fun):
    """A simple memoize decorator for functions supporting positional args."""
    @wraps(fun)
    def wrapper(*args, **kwargs):
        key = (args, frozenset(sorted(kwargs.items())))
        try:
            return cache[key]
        except KeyError:
            ret = cache[key] = fun(*args, **kwargs)
        return ret
    cache = {}
    return wrapper

Tests:

import unittest

class TestMemoize(unittest.TestCase):
    def test_it(self):
        @memoize
        def foo(*args, **kwargs):
            "foo docstring"
            calls.append(None)
            return (args, kwargs)

        calls = []
        # no args
        for x in range(2):
            ret = foo()
            expected = ((), {})
            self.assertEqual(ret, expected)
            self.assertEqual(len(calls), 1)
        # with args
        for x in range(2):
            ret = foo(1)
            expected = ((1, ), {})
            self.assertEqual(ret, expected)
            self.assertEqual(len(calls), 2)
        # with args + kwargs
        for x in range(2):
            ret = foo(1, bar=2)
            expected = ((1, ), {'bar': 2})
            self.assertEqual(ret, expected)
            self.assertEqual(len(calls), 3)
        self.assertEqual(foo.__doc__, "foo docstring")

unittest.main()

This works as long as you don't pass an unhashable type (e.g. dict) as argument. I don't have a solution for that but collections.lru_cache() implementation might have. See _make_key() function here: http://code.activestate.com/recipes/578078/