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# -*- test-case-name: twisted.test.test_nooldstyle -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Utilities to assist in the "flag day" new-style object transition.
"""
from __future__ import absolute_import, division
import types
from functools import wraps
from twisted.python.compat import _shouldEnableNewStyle, _PY3
def _replaceIf(condition, alternative):
"""
If C{condition}, replace this function with C{alternative}.
@param condition: A L{bool} which says whether this should be replaced.
@param alternative: An alternative function that will be swapped in instead
of the original, if C{condition} is truthy.
@return: A decorator.
"""
def decorator(func):
if condition is True:
call = alternative
elif condition is False:
call = func
else:
raise ValueError(("condition argument to _replaceIf requires a "
"bool, not {}").format(repr(condition)))
@wraps(func)
def wrapped(*args, **kwargs):
return call(*args, **kwargs)
return wrapped
return decorator
def passthru(arg):
"""
Return C{arg}. Do nothing.
@param arg: The arg to return.
@return: C{arg}
"""
return arg
def _ensureOldClass(cls):
"""
Ensure that C{cls} is an old-style class.
@param cls: The class to check.
@return: The class, if it is an old-style class.
@raises: L{ValueError} if it is a new-style class.
"""
if not type(cls) is types.ClassType:
from twisted.python.reflect import fullyQualifiedName
raise ValueError(
("twisted.python._oldstyle._oldStyle is being used to decorate a "
"new-style class ({cls}). This should only be used to "
"decorate old-style classes.").format(
cls=fullyQualifiedName(cls)))
return cls
@_replaceIf(_PY3, passthru)
@_replaceIf(not _shouldEnableNewStyle(), _ensureOldClass)
def _oldStyle(cls):
"""
A decorator which conditionally converts old-style classes to new-style
classes. If it is Python 3, or if the C{TWISTED_NEWSTYLE} environment
variable has a falsey (C{no}, C{false}, C{False}, or C{0}) value in the
environment, this decorator is a no-op.
@param cls: An old-style class to convert to new-style.
@type cls: L{types.ClassType}
@return: A new-style version of C{cls}.
"""
_ensureOldClass(cls)
_bases = cls.__bases__ + (object,)
return type(cls.__name__, _bases, cls.__dict__)
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