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85 lines
2.9 KiB
85 lines
2.9 KiB
# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
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# This implementation of the immutable decorator is for python 3.6,
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# which doesn't have Context Variables. This implementation is somewhat
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# costly for classes with slots, as it adds a __dict__ to them.
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import inspect
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class _Immutable:
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"""Immutable mixin class"""
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# Note we MUST NOT have __slots__ as that causes
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#
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# TypeError: multiple bases have instance lay-out conflict
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#
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# when we get mixed in with another class with slots. When we
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# get mixed into something with slots, it effectively adds __dict__ to
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# the slots of the other class, which allows attribute setting to work,
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# albeit at the cost of the dictionary.
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def __setattr__(self, name, value):
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if not hasattr(self, '_immutable_init') or \
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self._immutable_init is not self:
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raise TypeError("object doesn't support attribute assignment")
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else:
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super().__setattr__(name, value)
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def __delattr__(self, name):
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if not hasattr(self, '_immutable_init') or \
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self._immutable_init is not self:
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raise TypeError("object doesn't support attribute assignment")
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else:
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super().__delattr__(name)
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def _immutable_init(f):
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def nf(*args, **kwargs):
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try:
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# Are we already initializing an immutable class?
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previous = args[0]._immutable_init
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except AttributeError:
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# We are the first!
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previous = None
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object.__setattr__(args[0], '_immutable_init', args[0])
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try:
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# call the actual __init__
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f(*args, **kwargs)
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finally:
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if not previous:
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# If we started the initialzation, establish immutability
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# by removing the attribute that allows mutation
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object.__delattr__(args[0], '_immutable_init')
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nf.__signature__ = inspect.signature(f)
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return nf
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def immutable(cls):
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if _Immutable in cls.__mro__:
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# Some ancestor already has the mixin, so just make sure we keep
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# following the __init__ protocol.
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cls.__init__ = _immutable_init(cls.__init__)
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if hasattr(cls, '__setstate__'):
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cls.__setstate__ = _immutable_init(cls.__setstate__)
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ncls = cls
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else:
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# Mixin the Immutable class and follow the __init__ protocol.
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class ncls(_Immutable, cls):
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@_immutable_init
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def __init__(self, *args, **kwargs):
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super().__init__(*args, **kwargs)
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if hasattr(cls, '__setstate__'):
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@_immutable_init
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def __setstate__(self, *args, **kwargs):
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super().__setstate__(*args, **kwargs)
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# make ncls have the same name and module as cls
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ncls.__name__ = cls.__name__
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ncls.__qualname__ = cls.__qualname__
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ncls.__module__ = cls.__module__
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return ncls
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