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