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# copyright 2003-2011 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
#
# This file is part of logilab-common.
#
# logilab-common is free software: you can redistribute it and/or modify it under
# the terms of the GNU Lesser General Public License as published by the Free
# Software Foundation, either version 2.1 of the License, or (at your option) any
# later version.
#
# logilab-common is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License along
# with logilab-common. If not, see <http://www.gnu.org/licenses/>.
"""Bases class for interfaces to provide 'light' interface handling.
TODO:
_ implements a check method which check that an object implements the interface
_ Attribute objects
This module requires at least python 2.2
"""
__docformat__ = "restructuredtext en"
class Interface(object):
"""Base class for interfaces."""
@classmethod
def is_implemented_by(cls, instance: type) -> bool:
return implements(instance, cls)
def implements(obj: type, interface: type) -> bool:
"""Return true if the give object (maybe an instance or class) implements
the interface.
"""
kimplements = getattr(obj, "__implements__", ())
if not isinstance(kimplements, (list, tuple)):
kimplements = (kimplements,)
for implementedinterface in kimplements:
if issubclass(implementedinterface, interface):
return True
return False
def extend(klass: type, interface: type, _recurs: bool = False) -> None:
"""Add interface to klass'__implements__ if not already implemented in.
If klass is subclassed, ensure subclasses __implements__ it as well.
NOTE: klass should be e new class.
"""
if not implements(klass, interface):
try:
kimplements = klass.__implements__ # type: ignore
kimplementsklass = type(kimplements)
kimplements = list(kimplements)
except AttributeError:
kimplementsklass = tuple
kimplements = []
kimplements.append(interface)
klass.__implements__ = kimplementsklass(kimplements) # type: ignore
for subklass in klass.__subclasses__():
extend(subklass, interface, _recurs=True)
elif _recurs:
for subklass in klass.__subclasses__():
extend(subklass, interface, _recurs=True)
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