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#
# Copyright (c) 2006, 2007 Canonical
#
# Written by Gustavo Niemeyer <gustavo@niemeyer.net>
#
# This file is part of Storm Object Relational Mapper.
#
# Storm 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.
#
# Storm 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 this program. If not, see <http://www.gnu.org/licenses/>.
#
import weakref
from storm import has_cextensions
__all__ = ["EventSystem"]
class EventSystem(object):
"""A system for managing hooks that are called when events are emitted.
Hooks are callables that take the event system C{owner} as their first
argument, followed by the arguments passed when emitting the event,
followed by any additional C{data} arguments given when registering the
hook.
Hooks registered for a given event C{name} are stored without ordering:
no particular call order may be assumed when an event is emitted.
"""
def __init__(self, owner):
"""
@param owner: The object that owns this event system. It is passed
as the first argument to each hook function.
"""
self._owner_ref = weakref.ref(owner)
self._hooks = {}
def hook(self, name, callback, *data):
"""Register a hook.
@param name: The name of the event for which this hook should be
called.
@param callback: A callable which should be called when the event is
emitted.
@param data: Additional arguments to pass to the callable, after the
C{owner} and any arguments passed when emitting the event.
"""
callbacks = self._hooks.get(name)
if callbacks is None:
self._hooks.setdefault(name, set()).add((callback, data))
else:
callbacks.add((callback, data))
def unhook(self, name, callback, *data):
"""Unregister a hook.
This ignores attempts to unregister hooks that were not already
registered.
@param name: The name of the event for which this hook should no
longer be called.
@param callback: The callable to unregister.
@param data: Additional arguments that were passed when registering
the callable.
"""
callbacks = self._hooks.get(name)
if callbacks is not None:
callbacks.discard((callback, data))
def emit(self, name, *args):
"""Emit an event, calling any registered hooks.
@param name: The name of the event.
@param args: Additional arguments to pass to hooks.
"""
owner = self._owner_ref()
if owner is not None:
callbacks = self._hooks.get(name)
if callbacks:
for callback, data in tuple(callbacks):
if callback(owner, *(args+data)) is False:
callbacks.discard((callback, data))
if has_cextensions:
from storm.cextensions import EventSystem
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