from functools import partial class memoize(object): """cache the return value of a method This class is meant to be used as a decorator of methods. The return value from a given method invocation will be cached on the instance whose method was invoked. All arguments passed to a method decorated with memoize must be hashable. If a memoized method is invoked directly on its class the result will not be cached. Instead the method will be invoked like a static method: class Obj(object): @memoize def add_to(self, arg): return self + arg Obj.add_to(1) # not enough arguments Obj.add_to(1, 2) # returns 3, result is not cached """ def __init__(self, func): self.func = func def __get__(self, obj, objtype=None): if obj is None: return self.func return partial(self, obj) def __call__(self, *args, **kw): obj = args[0] try: cache = obj.__cache except AttributeError: cache = obj.__cache = {} key = (self.func, args[1:], frozenset(kw.items())) try: res = cache[key] except KeyError: res = cache[key] = self.func(*args, **kw) return res if __name__ == "__main__": # example usage class Test(object): v = 0 @memoize def inc_add(self, arg): self.v += 1 return self.v + arg t = Test() assert t.inc_add(2) == t.inc_add(2) assert Test.inc_add(t, 2) != Test.inc_add(t, 2)