对象中的 Python 缓存

Question

我创建了一个名为“Frame”的对象

class Frame:
    def __init__(self, image):
      self.image = image

    def gray(self):
      return cv2.cvtColor(self.image, cv2.COLOR_BGR2GRAY)

一些操作，例如gray()，很昂贵。我想将结果缓存在实例中，以便后续调用不必重新计算它。最干净的方法是什么？

Answer 1

金字塔使用 this fantastic @reify decorator :

class reify(object):
    """ Use as a class method decorator.  It operates almost exactly like the
    Python ``@property`` decorator, but it puts the result of the method it
    decorates into the instance dict after the first call, effectively
    replacing the function it decorates with an instance variable.  It is, in
    Python parlance, a non-data descriptor.  An example:

    .. code-block:: python

       class Foo(object):
           @reify
           def jammy(self):
               print('jammy called')
               return 1

    And usage of Foo:

    >>> f = Foo()
    >>> v = f.jammy
    'jammy called'
    >>> print(v)
    1
    >>> f.jammy
    1
    >>> # jammy func not called the second time; it replaced itself with 1
    """
    def __init__(self, wrapped):
        self.wrapped = wrapped
        try:
            self.__doc__ = wrapped.__doc__
        except: # pragma: no cover
            pass

    def __get__(self, inst, objtype=None):
        if inst is None:
            return self
        val = self.wrapped(inst)
        setattr(inst, self.wrapped.__name__, val)
        return val

文档字符串不言自明。 =)