35 lines
1.1 KiB
Python
35 lines
1.1 KiB
Python
# Copyright (C) 2013-2014 Eygene A. Ryabinkin and contributors
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#
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# Collection of classes that implement const-like behaviour
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# for various objects.
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import copy
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class ConstProxy:
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"""Implements read-only access to a given object
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that can be attached to each instance only once."""
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def __init__(self):
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self.__dict__['__source'] = None
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def __getattr__(self, name):
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src = self.__dict__['__source']
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if src is None:
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raise ValueError("using non-initialized ConstProxy() object")
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return copy.deepcopy(getattr(src, name))
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def __setattr__(self, name, value):
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raise AttributeError("tried to set '%s' to '%s' for constant object" %
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(name, value))
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def __delattr__(self, name):
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raise RuntimeError("tried to delete field '%s' from constant object" %
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name)
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def set_source(self, source):
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""" Sets source object for this instance. """
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if self.__dict__['__source'] is not None:
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raise ValueError("source object is already set")
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self.__dict__['__source'] = source
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