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 import threading
   9
  10
  11 class cached_property(object):
  12     """ A property that is only computed once per instance and then replaces
  13         itself with an ordinary attribute. Deleting the attribute resets the
  14         property.
  15
  16         Source: https://github.com/bottlepy/bottle/commit/fa7733e075da0d790d809aa3d2f53071897e6f76
  17         """
  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         value = obj.__dict__[self.func.__name__] = self.func(obj)
  27         return value
  28
  29
  30 class threaded_cached_property(cached_property):
  31     """ A cached_property version for use in environments where multiple
  32         threads might concurrently try to access the property.
  33         """
  34     def __init__(self, func):
  35         super(threaded_cached_property, self).__init__(func)
  36         self.lock = threading.RLock()
  37
  38     def __get__(self, obj, cls):
  39         with self.lock:
  40             # Double check if the value was computed before the lock was
  41             # acquired.
  42             prop_name = self.func.__name__
  43             if prop_name in obj.__dict__:
  44                 return obj.__dict__[prop_name]
  45
  46             # If not, do the calculation and release the lock.
  47             return super(threaded_cached_property, self).__get__(obj, cls)