chromium/third_party/blink/tools/blinkpy/common/memoized.py

# Copyright (c) 2010 Google Inc. All rights reserved.
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# Python does not (yet) seem to provide automatic memoization.  So we've
# written a small decorator to do so.

import functools


class memoized(object):
    def __init__(self, function):
        self._function = function
        self._results_cache = {}

    def __call__(self, *args):
        try:
            return self._results_cache[args]
        except KeyError:
            result = self._function(*args)
            self._results_cache[args] = result
            return result
        except TypeError as error:
            raise TypeError('Cannot call memoized function %s with unhashable '
                            'arguments: %s' %
                            (self._function.__name__, str(error)))

    # Use python "descriptor" protocol __get__ to appear
    # invisible during property access.
    def __get__(self, instance, owner):
        # Imagine we have a class, Foo, that has a @memoized method, bar(). So
        # that foo.bar() works we need to bind the underlying instance via
        # functools.partial, but we also want cache_clear() to work so we
        # monkey-patch it on top.
        wrapper = functools.partial(self.__call__, instance)
        wrapper.cache_clear = self.cache_clear
        return wrapper

    def cache_clear(self):
        self._results_cache = {}