cached_property.py

   1 # -*- coding: utf-8 -*-
   2
   3 __author__ = 'Daniel Greenfeld'
   4 __email__ = 'pydanny@gmail.com'
   5 __version__ = '0.1.5'
   6 __license__ = 'BSD'
   7
   8 from time import time
   9 import threading
  10
  11
  12 class cached_property(object):
  13     """ A property that is only computed once per instance and then replaces
  14         itself with an ordinary attribute. Deleting the attribute resets the
  15         property.
  16
  17         Source: https://github.com/bottlepy/bottle/commit/fa7733e075da0d790d809aa3d2f53071897e6f76
  18         """  # noqa
  19
  20     def __init__(self, ttl=None):
  21         ttl_or_func = ttl
  22         self.ttl = None
  23         if callable(ttl_or_func):
  24             self.prepare_func(ttl_or_func)
  25         else:
  26             self.ttl = ttl_or_func
  27
  28     def prepare_func(self, func, doc=None):
  29         '''Prepare to cache object method.'''
  30         self.func = func
  31         self.__doc__ = doc or func.__doc__
  32         self.__name__ = func.__name__
  33         self.__module__ = func.__module__
  34
  35     def __call__(self, func, doc=None):
  36         self.prepare_func(func, doc)
  37         return self
  38
  39     def __get__(self, obj, cls):
  40         if obj is None:
  41             return self
  42
  43         now = time()
  44         try:
  45             value, last_update = obj._cache[self.__name__]
  46             if self.ttl and self.ttl > 0 and now - last_update > self.ttl:
  47                 raise AttributeError
  48         except (KeyError, AttributeError):
  49             value = self.func(obj)
  50             try:
  51                 cache = obj._cache
  52             except AttributeError:
  53                 cache = obj._cache = {}
  54             cache[self.__name__] = (value, now)
  55
  56         return value
  57
  58     def __delattr__(self, name):
  59         print(name)
  60
  61
  62 class threaded_cached_property(cached_property):
  63     """ A cached_property version for use in environments where multiple
  64         threads might concurrently try to access the property.
  65         """
  66     def __init__(self, ttl=None):
  67         super(threaded_cached_property, self).__init__(ttl)
  68         self.lock = threading.RLock()
  69
  70     def __get__(self, obj, cls):
  71         with self.lock:
  72             # Double check if the value was computed before the lock was
  73             # acquired.
  74             prop_name = self.__name__
  75             if hasattr(obj, '_cache') and prop_name in obj._cache:
  76                 return obj._cache[prop_name][0]
  77
  78             # If not, do the calculation and release the lock.
  79             return super(threaded_cached_property, self).__get__(obj, cls)