python resettable instance method memoization decorator

Question

I\'m attempting to build a decorator for an instance method of a class that will memoize the result. (This has been done a million times before) However, I\'d like the optio

Answer 1

Rather than trying to work out the mechanics of your implementation, I've taken the memoized decorator class from PythonDecoratorLibrary, and have modified it to add reset. Below is the result; the trick I've used is to add a callable reset attribute to the decorated function itself.

    class memoized2(object):
       """Decorator that caches a function's return value each time it is called.
       If called later with the same arguments, the cached value is returned, and
       not re-evaluated.
       """
       def __init__(self, func):
          self.func = func
          self.cache = {}
       def __call__(self, *args):
          try:
             return self.cache[args]
          except KeyError:
             value = self.func(*args)
             self.cache[args] = value
             return value
          except TypeError:
             # uncachable -- for instance, passing a list as an argument.
             # Better to not cache than to blow up entirely.
             return self.func(*args)
       def __repr__(self):
          """Return the function's docstring."""
          return self.func.__doc__
       def __get__(self, obj, objtype):
          """Support instance methods."""
          fn = functools.partial(self.__call__, obj)
          fn.reset = self._reset
          return fn
       def _reset(self):
          self.cache = {}


    class my_class:
        @memoized2
        def my_func(self, val):
            print "in my_func"
            time.sleep(2)
            return val


    c = my_class()

    print "should take time"
    print c.my_func(55)
    print

    print "should be instant"
    print c.my_func(55)
    print

    c.my_func.reset()

    print "should take time"
    print c.my_func(55)