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"""
Copyright (C) 2013-2014 Eygene A. Ryabinkin and contributors
Collection of classes that implement const-like behaviour
for various objects.
"""
import copy
class ConstProxy:
"""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 is 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'] is not None:
raise ValueError("source object is already set")
self.__dict__['__source'] = source
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