1 ### -*- coding: utf-8 -*- ####################################################

     2 ##############################################################################

     3 #

     4 # Copyright (c) 2012 Thierry Florac <tflorac AT ulthar.net>

     5 # All Rights Reserved.

     6 #

     7 # This software is subject to the provisions of the Zope Public License,

     8 # Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.

     9 # THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED

    10 # WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

    11 # WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS

    12 # FOR A PARTICULAR PURPOSE.

    13 #

    14 ##############################################################################

    15 

    16 

    17 # import standard packages

    18 

    19 # import Zope3 interfaces

    20 

    21 # import local interfaces

    22 

    23 # import Zope3 packages

    24 

    25 # import local packages

    26 

    27 

    28 class cached(object):

    29     """Custom property decorator to define a property or function

    30     which is calculated only once

    31        

    32     When applied on a function, caching is based on input arguments

    33     """

    34 

    35     def __init__(self, function):

    36         self._function = function

    37         self._cache = {}

    38 

    39     def __call__(self, *args):

    40         try:

    41             return self._cache[args]

    42         except KeyError:

    43             self._cache[args] = self._function(*args)

    44             return self._cache[args]

    45 

    46     def expire(self, *args):

    47         del self._cache[args]

    48 

    49 

    50 class cached_property(object):

    51     """A read-only @property decorator that is only evaluated once. The value is cached

    52     on the object itself rather than the function or class; this should prevent

    53     memory leakage.

    54     """

    55     def __init__(self, fget, doc=None):

    56         self.fget = fget

    57         self.__doc__ = doc or fget.__doc__

    58         self.__name__ = fget.__name__

    59         self.__module__ = fget.__module__

    60 

    61     def __get__(self, obj, cls):

    62         if obj is None:

    63             return self

    64         obj.__dict__[self.__name__] = result = self.fget(obj)

    65         return result