# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license # This implementation of the immutable decorator requires python >= # 3.7, and is significantly more storage efficient when making classes # with slots immutable. It's also faster. import contextvars import inspect _in__init__ = contextvars.ContextVar("_immutable_in__init__", default=False) class _Immutable: """Immutable mixin class""" # We set slots to the empty list to say "we don't have any attributes". # We do this so that if we're mixed in with a class with __slots__, we # don't cause a __dict__ to be added which would waste space. __slots__ = () def __setattr__(self, name, value): if _in__init__.get() is not self: raise TypeError("object doesn't support attribute assignment") else: super().__setattr__(name, value) def __delattr__(self, name): if _in__init__.get() is not self: raise TypeError("object doesn't support attribute assignment") else: super().__delattr__(name) def _immutable_init(f): def nf(*args, **kwargs): previous = _in__init__.set(args[0]) try: # call the actual __init__ f(*args, **kwargs) finally: _in__init__.reset(previous) nf.__signature__ = inspect.signature(f) return nf def immutable(cls): if _Immutable in cls.__mro__: # Some ancestor already has the mixin, so just make sure we keep # following the __init__ protocol. cls.__init__ = _immutable_init(cls.__init__) if hasattr(cls, "__setstate__"): cls.__setstate__ = _immutable_init(cls.__setstate__) ncls = cls else: # Mixin the Immutable class and follow the __init__ protocol. class ncls(_Immutable, cls): # We have to do the __slots__ declaration here too! __slots__ = () @_immutable_init def __init__(self, *args, **kwargs): super().__init__(*args, **kwargs) if hasattr(cls, "__setstate__"): @_immutable_init def __setstate__(self, *args, **kwargs): super().__setstate__(*args, **kwargs) # make ncls have the same name and module as cls ncls.__name__ = cls.__name__ ncls.__qualname__ = cls.__qualname__ ncls.__module__ = cls.__module__ return ncls