indico/util/contextManager.py

   1 # This file is part of Indico.
   2 # Copyright (C) 2002 - 2015 European Organization for Nuclear Research (CERN).
   3 #
   4 # Indico is free software; you can redistribute it and/or
   5 # modify it under the terms of the GNU General Public License as
   6 # published by the Free Software Foundation; either version 3 of the
   7 # License, or (at your option) any later version.
   8 #
   9 # Indico is distributed in the hope that it will be useful, but
  10 # WITHOUT ANY WARRANTY; without even the implied warranty of
  11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 # General Public License for more details.
  13 #
  14 # You should have received a copy of the GNU General Public License
  15 # along with Indico; if not, see <http://www.gnu.org/licenses/>.
  16
  17 """
  18 Defines the ContextManager, which provides a global access namespace for
  19 storing runtime information
  20 """
  21
  22 import threading
  23
  24
  25 class DummyDict(object):
  26     """
  27     A context that doesn't react, much like a Null Object
  28     """
  29
  30     def __init__(self):
  31         pass
  32
  33     def _dummyMethod(*args, **__):
  34         """
  35         this method just does nothing, accepting
  36         whatever arguments are passed to it
  37         """
  38         return None
  39
  40     def __getattr__(self, name):
  41         return self._dummyMethod
  42
  43     def __setattr__(self, name, value):
  44         return None
  45
  46     def __nonzero__(self):
  47         return False
  48
  49     def __str__(self):
  50         return "<DummyDict>"
  51
  52
  53 class Context(threading.local):
  54     def __init__(self, **kwargs):
  55         self.__dict__.update(kwargs)
  56
  57     def __contains__(self, elem):
  58         return elem in self.__dict__
  59
  60     def __getitem__(self, elem):
  61         return self.get(elem)
  62
  63     def get(self, elem, default=DummyDict()):
  64         if elem in self.__dict__:
  65             return self.__dict__[elem]
  66         else:
  67             return default
  68
  69     def __setitem__(self, elem, value):
  70         self.__dict__[elem] = value
  71
  72     def __delitem__(self, elem):
  73         del self.__dict__[elem]
  74
  75     def clear(self):
  76         self.__dict__.clear()
  77
  78     def setdefault(self, name, default):
  79         return self.__dict__.setdefault(name, default)
  80
  81
  82 class ContextManager(object):
  83     """
  84     A context manager provides a global access namespace (singleton) for storing
  85     run-time information.
  86     """
  87
  88     _context = Context()
  89
  90     def __init__(self):
  91         pass
  92
  93     @classmethod
  94     def destroy(cls):
  95         """
  96         destroy the context
  97         """
  98         cls._context.clear()
  99
 100     @classmethod
 101     def get(cls, elem=None, default=DummyDict()):
 102         """
 103         If no set has been done over the variable before,
 104         a dummy context will be returned.
 105         """
 106         if elem is None:
 107             return cls._context
 108         else:
 109             return cls._context.get(elem, default)
 110
 111     @classmethod
 112     def set(cls, elem, value):
 113         cls._context[elem] = value
 114         return cls.get(elem)
 115
 116     @classmethod
 117     def setdefault(cls, name, default):
 118         """
 119         If no set has been done over the variable before,
 120         a default value is *set* and *returned*
 121         """
 122         return cls._context.setdefault(name, default)
 123
 124     @classmethod
 125     def delete(cls, name, silent=False):
 126         try:
 127             del cls._context[name]
 128         except KeyError:
 129             if not silent:
 130                 raise