cached_property.py

   1 # -*- coding: utf-8 -*-
   2
   3 __author__ = 'Daniel Greenfeld'
   4 __email__ = 'pydanny@gmail.com'
   5 __version__ = '1.0.0'
   6 __license__ = 'BSD'
   7
   8 from time import time
   9 import threading
  10
  11
  12 class cached_property(object):
  13     """
  14     A property that is only computed once per instance and then replaces itself
  15     with an ordinary attribute. Deleting the attribute resets the property.
  16     Source: https://github.com/bottlepy/bottle/commit/fa7733e075da0d790d809aa3d2f53071897e6f76
  17     """  # noqa
  18
  19     def __init__(self, func):
  20         self.__doc__ = getattr(func, '__doc__')
  21         self.func = func
  22
  23     def __get__(self, obj, cls):
  24         if obj is None:
  25             return self
  26         return obj.__dict__.setdefault(self.func.__name__, self.func(obj))
  27
  28
  29 # Leave for backwards compatibility
  30 threaded_cached_property = cached_property
  31
  32
  33 class cached_property_with_ttl(object):
  34     """
  35     A property that is only computed once per instance and then replaces itself
  36     with an ordinary attribute. Setting the ttl to a number expresses how long
  37     the property will last before being timed out.
  38     """
  39
  40     def __init__(self, ttl=None):
  41         ttl_or_func = ttl
  42         self.ttl = None
  43         if callable(ttl_or_func):
  44             self.prepare_func(ttl_or_func)
  45         else:
  46             self.ttl = ttl_or_func
  47
  48     def prepare_func(self, func, doc=None):
  49         '''Prepare to cache object method.'''
  50         self.func = func
  51         self.__doc__ = doc or func.__doc__
  52         self.__name__ = func.__name__
  53         self.__module__ = func.__module__
  54
  55     def __call__(self, func, doc=None):
  56         self.prepare_func(func, doc)
  57         return self
  58
  59     def __get__(self, obj, cls):
  60         if obj is None:
  61             return self
  62
  63         now = time()
  64         try:
  65             value, last_update = obj._cache[self.__name__]
  66             if self.ttl and self.ttl > 0 and now - last_update > self.ttl:
  67                 raise AttributeError
  68         except (KeyError, AttributeError):
  69             value = self.func(obj)
  70             try:
  71                 cache = obj._cache
  72             except AttributeError:
  73                 cache = obj._cache = {}
  74             cache[self.__name__] = (value, now)
  75
  76         return value
  77
  78     def __delete__(self, obj):
  79         try:
  80             del obj._cache[self.__name__]
  81         except (KeyError, AttributeError):
  82             pass
  83
  84 # Aliases to make cached_property_with_ttl easier to use
  85 cached_property_ttl = cached_property_with_ttl
  86 timed_cached_property = cached_property_with_ttl
  87
  88
  89 class threaded_cached_property_with_ttl(cached_property_with_ttl):
  90     """
  91     A cached_property version for use in environments where multiple threads
  92     might concurrently try to access the property.
  93     """
  94
  95     def __init__(self, ttl=None):
  96         super(threaded_cached_property_with_ttl, self).__init__(ttl)
  97         self.lock = threading.RLock()
  98
  99     def __get__(self, obj, cls):
 100         with self.lock:
 101             # Double check if the value was computed before the lock was
 102             # acquired.
 103             prop_name = self.__name__
 104             if hasattr(obj, '_cache') and prop_name in obj._cache:
 105                 return obj._cache[prop_name][0]
 106
 107             # If not, do the calculation and release the lock.
 108             return super(threaded_cached_property_with_ttl, self).__get__(obj,
 109                                                                           cls)
 110
 111 # Alias to make threaded_cached_property_with_ttl easier to use
 112 threaded_cached_property_ttl = threaded_cached_property_with_ttl
 113 timed_threaded_cached_property = threaded_cached_property_with_ttl