77 lines
2.4 KiB
Python
77 lines
2.4 KiB
Python
# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
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# This implementation of the immutable decorator requires python >=
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# 3.7, and is significantly more storage efficient when making classes
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# with slots immutable. It's also faster.
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import contextvars
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import inspect
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_in__init__ = contextvars.ContextVar("_immutable_in__init__", default=False)
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class _Immutable:
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"""Immutable mixin class"""
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# We set slots to the empty list to say "we don't have any attributes".
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# We do this so that if we're mixed in with a class with __slots__, we
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# don't cause a __dict__ to be added which would waste space.
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__slots__ = ()
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def __setattr__(self, name, value):
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if _in__init__.get() 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 _in__init__.get() 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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previous = _in__init__.set(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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_in__init__.reset(previous)
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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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# We have to do the __slots__ declaration here too!
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__slots__ = ()
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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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