290 lines
9.3 KiB
Python
290 lines
9.3 KiB
Python
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# event/base.py
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# Copyright (C) 2005-2018 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: http://www.opensource.org/licenses/mit-license.php
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"""Base implementation classes.
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The public-facing ``Events`` serves as the base class for an event interface;
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its public attributes represent different kinds of events. These attributes
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are mirrored onto a ``_Dispatch`` class, which serves as a container for
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collections of listener functions. These collections are represented both
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at the class level of a particular ``_Dispatch`` class as well as within
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instances of ``_Dispatch``.
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"""
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from __future__ import absolute_import
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import weakref
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from .. import util
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from .attr import _JoinedListener, \
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_EmptyListener, _ClsLevelDispatch
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_registrars = util.defaultdict(list)
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def _is_event_name(name):
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return not name.startswith('_') and name != 'dispatch'
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class _UnpickleDispatch(object):
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"""Serializable callable that re-generates an instance of
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:class:`_Dispatch` given a particular :class:`.Events` subclass.
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"""
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def __call__(self, _instance_cls):
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for cls in _instance_cls.__mro__:
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if 'dispatch' in cls.__dict__:
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return cls.__dict__['dispatch'].\
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dispatch_cls._for_class(_instance_cls)
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else:
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raise AttributeError("No class with a 'dispatch' member present.")
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class _Dispatch(object):
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"""Mirror the event listening definitions of an Events class with
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listener collections.
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Classes which define a "dispatch" member will return a
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non-instantiated :class:`._Dispatch` subclass when the member
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is accessed at the class level. When the "dispatch" member is
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accessed at the instance level of its owner, an instance
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of the :class:`._Dispatch` class is returned.
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A :class:`._Dispatch` class is generated for each :class:`.Events`
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class defined, by the :func:`._create_dispatcher_class` function.
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The original :class:`.Events` classes remain untouched.
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This decouples the construction of :class:`.Events` subclasses from
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the implementation used by the event internals, and allows
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inspecting tools like Sphinx to work in an unsurprising
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way against the public API.
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"""
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# in one ORM edge case, an attribute is added to _Dispatch,
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# so __dict__ is used in just that case and potentially others.
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__slots__ = '_parent', '_instance_cls', '__dict__', '_empty_listeners'
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_empty_listener_reg = weakref.WeakKeyDictionary()
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def __init__(self, parent, instance_cls=None):
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self._parent = parent
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self._instance_cls = instance_cls
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if instance_cls:
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try:
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self._empty_listeners = self._empty_listener_reg[instance_cls]
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except KeyError:
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self._empty_listeners = \
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self._empty_listener_reg[instance_cls] = dict(
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(ls.name, _EmptyListener(ls, instance_cls))
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for ls in parent._event_descriptors
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)
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else:
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self._empty_listeners = {}
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def __getattr__(self, name):
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# assign EmptyListeners as attributes on demand
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# to reduce startup time for new dispatch objects
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try:
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ls = self._empty_listeners[name]
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except KeyError:
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raise AttributeError(name)
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else:
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setattr(self, ls.name, ls)
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return ls
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@property
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def _event_descriptors(self):
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for k in self._event_names:
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yield getattr(self, k)
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def _for_class(self, instance_cls):
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return self.__class__(self, instance_cls)
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def _for_instance(self, instance):
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instance_cls = instance.__class__
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return self._for_class(instance_cls)
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@property
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def _listen(self):
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return self._events._listen
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def _join(self, other):
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"""Create a 'join' of this :class:`._Dispatch` and another.
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This new dispatcher will dispatch events to both
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:class:`._Dispatch` objects.
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"""
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if '_joined_dispatch_cls' not in self.__class__.__dict__:
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cls = type(
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"Joined%s" % self.__class__.__name__,
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(_JoinedDispatcher, ), {'__slots__': self._event_names}
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)
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self.__class__._joined_dispatch_cls = cls
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return self._joined_dispatch_cls(self, other)
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def __reduce__(self):
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return _UnpickleDispatch(), (self._instance_cls, )
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def _update(self, other, only_propagate=True):
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"""Populate from the listeners in another :class:`_Dispatch`
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object."""
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for ls in other._event_descriptors:
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if isinstance(ls, _EmptyListener):
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continue
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getattr(self, ls.name).\
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for_modify(self)._update(ls, only_propagate=only_propagate)
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def _clear(self):
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for ls in self._event_descriptors:
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ls.for_modify(self).clear()
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class _EventMeta(type):
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"""Intercept new Event subclasses and create
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associated _Dispatch classes."""
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def __init__(cls, classname, bases, dict_):
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_create_dispatcher_class(cls, classname, bases, dict_)
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return type.__init__(cls, classname, bases, dict_)
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def _create_dispatcher_class(cls, classname, bases, dict_):
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"""Create a :class:`._Dispatch` class corresponding to an
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:class:`.Events` class."""
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# there's all kinds of ways to do this,
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# i.e. make a Dispatch class that shares the '_listen' method
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# of the Event class, this is the straight monkeypatch.
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if hasattr(cls, 'dispatch'):
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dispatch_base = cls.dispatch.__class__
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else:
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dispatch_base = _Dispatch
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event_names = [k for k in dict_ if _is_event_name(k)]
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dispatch_cls = type("%sDispatch" % classname,
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(dispatch_base, ), {'__slots__': event_names})
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dispatch_cls._event_names = event_names
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dispatch_inst = cls._set_dispatch(cls, dispatch_cls)
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for k in dispatch_cls._event_names:
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setattr(dispatch_inst, k, _ClsLevelDispatch(cls, dict_[k]))
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_registrars[k].append(cls)
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for super_ in dispatch_cls.__bases__:
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if issubclass(super_, _Dispatch) and super_ is not _Dispatch:
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for ls in super_._events.dispatch._event_descriptors:
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setattr(dispatch_inst, ls.name, ls)
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dispatch_cls._event_names.append(ls.name)
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if getattr(cls, '_dispatch_target', None):
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cls._dispatch_target.dispatch = dispatcher(cls)
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def _remove_dispatcher(cls):
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for k in cls.dispatch._event_names:
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_registrars[k].remove(cls)
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if not _registrars[k]:
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del _registrars[k]
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class Events(util.with_metaclass(_EventMeta, object)):
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"""Define event listening functions for a particular target type."""
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@staticmethod
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def _set_dispatch(cls, dispatch_cls):
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# this allows an Events subclass to define additional utility
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# methods made available to the target via
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# "self.dispatch._events.<utilitymethod>"
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# @staticemethod to allow easy "super" calls while in a metaclass
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# constructor.
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cls.dispatch = dispatch_cls(None)
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dispatch_cls._events = cls
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return cls.dispatch
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@classmethod
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def _accept_with(cls, target):
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# Mapper, ClassManager, Session override this to
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# also accept classes, scoped_sessions, sessionmakers, etc.
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if hasattr(target, 'dispatch') and (
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isinstance(target.dispatch, cls.dispatch.__class__) or
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(
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isinstance(target.dispatch, type) and
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isinstance(target.dispatch, cls.dispatch.__class__)
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) or
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(
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isinstance(target.dispatch, _JoinedDispatcher) and
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isinstance(target.dispatch.parent, cls.dispatch.__class__)
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)
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):
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return target
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else:
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return None
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@classmethod
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def _listen(cls, event_key, propagate=False, insert=False, named=False):
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event_key.base_listen(propagate=propagate, insert=insert, named=named)
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@classmethod
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def _remove(cls, event_key):
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event_key.remove()
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@classmethod
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def _clear(cls):
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cls.dispatch._clear()
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class _JoinedDispatcher(object):
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"""Represent a connection between two _Dispatch objects."""
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__slots__ = 'local', 'parent', '_instance_cls'
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def __init__(self, local, parent):
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self.local = local
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self.parent = parent
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self._instance_cls = self.local._instance_cls
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def __getattr__(self, name):
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# assign _JoinedListeners as attributes on demand
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# to reduce startup time for new dispatch objects
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ls = getattr(self.local, name)
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jl = _JoinedListener(self.parent, ls.name, ls)
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setattr(self, ls.name, jl)
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return jl
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@property
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def _listen(self):
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return self.parent._listen
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class dispatcher(object):
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"""Descriptor used by target classes to
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deliver the _Dispatch class at the class level
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and produce new _Dispatch instances for target
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instances.
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"""
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def __init__(self, events):
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self.dispatch_cls = events.dispatch
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self.events = events
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def __get__(self, obj, cls):
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if obj is None:
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return self.dispatch_cls
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obj.__dict__['dispatch'] = disp = self.dispatch_cls._for_instance(obj)
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return disp
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