old_contents: # Copyright 2013 Eygene A. Ryabinkin.
  #
  # Collection of classes that implement const-like behaviour
  # for various objects.
  
  import copy
  
  class ConstProxy (object):
  	"""
  	Implements read-only access to a given object
  	that can be attached to each instance only once.
  
  	"""
  
  	def __init__ (self):
  		self.__dict__['__source'] = None
  
  
  	def __getattr__ (self, name):
  		src = self.__dict__['__source']
  		if src == None:
  			raise ValueError ("using non-initialized ConstProxy() object")
  		return copy.deepcopy (getattr (src, name))
  
  
  	def __setattr__ (self, name, value):
  		raise AttributeError ("tried to set '%s' to '%s' for constant object" % \
  		  (name, value))
  
  
  	def __delattr__ (self, name):
  		raise RuntimeError ("tried to delete field '%s' from constant object" % \
  		  (name))
  
  
  	def set_source (self, source):
  		""" Sets source object for this instance. """
  		if (self.__dict__['__source'] != None):
  			raise ValueError ("source object is already set")
  		self.__dict__['__source'] = source
  
new_contents: # Copyright (C) 2013-2014 Eygene A. Ryabinkin and contributors
  #
  # Collection of classes that implement const-like behaviour
  # for various objects.
  
  import copy
  
  class ConstProxy(object):
      """Implements read-only access to a given object
      that can be attached to each instance only once."""
  
      def __init__(self):
          self.__dict__['__source'] = None
  
  
      def __getattr__(self, name):
          src = self.__dict__['__source']
          if src == None:
              raise ValueError("using non-initialized ConstProxy() object")
          return copy.deepcopy(getattr(src, name))
  
  
      def __setattr__(self, name, value):
          raise AttributeError("tried to set '%s' to '%s' for constant object"% \
              (name, value))
  
  
      def __delattr__(self, name):
          raise RuntimeError("tried to delete field '%s' from constant object"% \
              (name))
  
  
      def set_source(self, source):
          """ Sets source object for this instance. """
          if (self.__dict__['__source'] != None):
              raise ValueError("source object is already set")
          self.__dict__['__source'] = source
  
subject: fix ident