220 lines
7.1 KiB
Python
220 lines
7.1 KiB
Python
# event/base.py
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# Copyright (C) 2005-2014 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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from .. import util
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from .attr import _JoinedDispatchDescriptor, \
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_EmptyListener, _DispatchDescriptor
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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, _parent_cls):
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for cls in _parent_cls.__mro__:
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if 'dispatch' in cls.__dict__:
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return cls.__dict__['dispatch'].dispatch_cls(_parent_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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_events = None
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"""reference the :class:`.Events` class which this
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:class:`._Dispatch` is created for."""
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def __init__(self, _parent_cls):
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self._parent_cls = _parent_cls
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@util.classproperty
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def _listen(cls):
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return cls._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, self.__class__), {}
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)
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for ls in _event_descriptors(self):
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setattr(cls, ls.name, _JoinedDispatchDescriptor(ls.name))
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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._parent_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 _event_descriptors(other):
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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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@util.hybridmethod
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def _clear(self):
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for attr in dir(self):
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if _is_event_name(attr):
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getattr(self, attr).for_modify(self).clear()
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def _event_descriptors(target):
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return [getattr(target, k) for k in dir(target) if _is_event_name(k)]
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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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dispatch_base = getattr(cls, 'dispatch', _Dispatch)
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dispatch_cls = type("%sDispatch" % classname,
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(dispatch_base, ), {})
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cls._set_dispatch(cls, dispatch_cls)
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for k in dict_:
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if _is_event_name(k):
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setattr(dispatch_cls, k, _DispatchDescriptor(cls, dict_[k]))
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_registrars[k].append(cls)
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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 dir(cls):
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if _is_event_name(k):
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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
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dispatch_cls._events = cls
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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) or
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isinstance(target.dispatch, type) and
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issubclass(target.dispatch, cls.dispatch)
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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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def __init__(self, local, parent):
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self.local = local
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self.parent = parent
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self._parent_cls = local._parent_cls
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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(cls)
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return disp
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