chrome/common/extensions/docs/server2/future.py

   1 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 # Use of this source code is governed by a BSD-style license that can be
   3 # found in the LICENSE file.
   4
   5 import sys
   6
   7 _no_value = object()
   8
   9
  10 class Gettable(object):
  11   '''Allows a Future to accept a callable as a delegate. Wraps |f| in a .Get
  12   interface required by Future.
  13   '''
  14   def __init__(self, f, *args):
  15     self._g = lambda: f(*args)
  16   def Get(self):
  17     return self._g()
  18
  19
  20 class Future(object):
  21   '''Stores a value, error, or delegate to be used later.
  22   '''
  23   def __init__(self, value=_no_value, delegate=None, exc_info=None):
  24     self._value = value
  25     self._delegate = delegate
  26     self._exc_info = exc_info
  27     if (self._value is _no_value and
  28         self._delegate is None and
  29         self._exc_info is None):
  30       raise ValueError('Must have either a value, error, or delegate.')
  31
  32   def Get(self):
  33     '''Gets the stored value, error, or delegate contents.
  34     '''
  35     if self._value is not _no_value:
  36       return self._value
  37     if self._exc_info is not None:
  38       self._Raise()
  39     try:
  40       self._value = self._delegate.Get()
  41       return self._value
  42     except:
  43       self._exc_info = sys.exc_info()
  44       self._Raise()
  45
  46   def _Raise(self):
  47     exc_info = self._exc_info
  48     raise exc_info[0], exc_info[1], exc_info[2]