# 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
