mirror of
https://github.com/janeczku/calibre-web
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556 lines
17 KiB
Python
556 lines
17 KiB
Python
# sqlalchemy/event.py
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# Copyright (C) 2005-2013 the SQLAlchemy authors and contributors <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 event API."""
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from . import util, exc
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from itertools import chain
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import weakref
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CANCEL = util.symbol('CANCEL')
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NO_RETVAL = util.symbol('NO_RETVAL')
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def listen(target, identifier, fn, *args, **kw):
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"""Register a listener function for the given target.
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e.g.::
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from sqlalchemy import event
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from sqlalchemy.schema import UniqueConstraint
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def unique_constraint_name(const, table):
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const.name = "uq_%s_%s" % (
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table.name,
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list(const.columns)[0].name
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)
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event.listen(
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UniqueConstraint,
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"after_parent_attach",
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unique_constraint_name)
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"""
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for evt_cls in _registrars[identifier]:
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tgt = evt_cls._accept_with(target)
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if tgt is not None:
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tgt.dispatch._listen(tgt, identifier, fn, *args, **kw)
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return
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raise exc.InvalidRequestError("No such event '%s' for target '%s'" %
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(identifier, target))
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def listens_for(target, identifier, *args, **kw):
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"""Decorate a function as a listener for the given target + identifier.
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e.g.::
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from sqlalchemy import event
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from sqlalchemy.schema import UniqueConstraint
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@event.listens_for(UniqueConstraint, "after_parent_attach")
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def unique_constraint_name(const, table):
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const.name = "uq_%s_%s" % (
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table.name,
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list(const.columns)[0].name
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)
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"""
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def decorate(fn):
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listen(target, identifier, fn, *args, **kw)
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return fn
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return decorate
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def remove(target, identifier, fn):
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"""Remove an event listener.
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Note that some event removals, particularly for those event dispatchers
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which create wrapper functions and secondary even listeners, may not yet
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be supported.
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"""
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for evt_cls in _registrars[identifier]:
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for tgt in evt_cls._accept_with(target):
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tgt.dispatch._remove(identifier, tgt, fn)
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return
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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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def __init__(self, _parent_cls):
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self._parent_cls = _parent_cls
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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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Once constructed, the joined dispatch will respond to new events
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added to this dispatcher, but may not be aware of events
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added to the other dispatcher after creation of the join. This is
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currently for performance reasons so that both dispatchers need
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not be "evaluated" fully on each call.
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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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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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cls.dispatch = dispatch_cls = type("%sDispatch" % classname,
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(dispatch_base, ), {})
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dispatch_cls._listen = cls._listen
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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(dict_[k]))
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_registrars[k].append(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(object):
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"""Define event listening functions for a particular target type."""
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__metaclass__ = _EventMeta
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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, target, identifier, fn, propagate=False, insert=False):
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if insert:
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getattr(target.dispatch, identifier).\
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for_modify(target.dispatch).insert(fn, target, propagate)
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else:
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getattr(target.dispatch, identifier).\
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for_modify(target.dispatch).append(fn, target, propagate)
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@classmethod
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def _remove(cls, target, identifier, fn):
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getattr(target.dispatch, identifier).remove(fn, target)
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@classmethod
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def _clear(cls):
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cls.dispatch._clear()
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class _DispatchDescriptor(object):
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"""Class-level attributes on :class:`._Dispatch` classes."""
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def __init__(self, fn):
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self.__name__ = fn.__name__
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self.__doc__ = fn.__doc__
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self._clslevel = weakref.WeakKeyDictionary()
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self._empty_listeners = weakref.WeakKeyDictionary()
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def _contains(self, cls, evt):
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return cls in self._clslevel and \
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evt in self._clslevel[cls]
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def insert(self, obj, target, propagate):
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assert isinstance(target, type), \
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"Class-level Event targets must be classes."
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stack = [target]
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while stack:
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cls = stack.pop(0)
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stack.extend(cls.__subclasses__())
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if cls is not target and cls not in self._clslevel:
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self.update_subclass(cls)
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else:
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if cls not in self._clslevel:
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self._clslevel[cls] = []
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self._clslevel[cls].insert(0, obj)
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def append(self, obj, target, propagate):
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assert isinstance(target, type), \
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"Class-level Event targets must be classes."
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stack = [target]
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while stack:
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cls = stack.pop(0)
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stack.extend(cls.__subclasses__())
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if cls is not target and cls not in self._clslevel:
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self.update_subclass(cls)
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else:
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if cls not in self._clslevel:
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self._clslevel[cls] = []
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self._clslevel[cls].append(obj)
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def update_subclass(self, target):
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if target not in self._clslevel:
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self._clslevel[target] = []
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clslevel = self._clslevel[target]
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for cls in target.__mro__[1:]:
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if cls in self._clslevel:
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clslevel.extend([
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fn for fn
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in self._clslevel[cls]
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if fn not in clslevel
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])
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def remove(self, obj, target):
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stack = [target]
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while stack:
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cls = stack.pop(0)
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stack.extend(cls.__subclasses__())
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if cls in self._clslevel:
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self._clslevel[cls].remove(obj)
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def clear(self):
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"""Clear all class level listeners"""
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for dispatcher in self._clslevel.values():
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dispatcher[:] = []
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def for_modify(self, obj):
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"""Return an event collection which can be modified.
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For _DispatchDescriptor at the class level of
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a dispatcher, this returns self.
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"""
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return self
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def __get__(self, obj, cls):
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if obj is None:
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return self
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elif obj._parent_cls in self._empty_listeners:
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ret = self._empty_listeners[obj._parent_cls]
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else:
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self._empty_listeners[obj._parent_cls] = ret = \
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_EmptyListener(self, obj._parent_cls)
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# assigning it to __dict__ means
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# memoized for fast re-access. but more memory.
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obj.__dict__[self.__name__] = ret
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return ret
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class _EmptyListener(object):
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"""Serves as a class-level interface to the events
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served by a _DispatchDescriptor, when there are no
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instance-level events present.
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Is replaced by _ListenerCollection when instance-level
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events are added.
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"""
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def __init__(self, parent, target_cls):
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if target_cls not in parent._clslevel:
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parent.update_subclass(target_cls)
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self.parent = parent
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self.parent_listeners = parent._clslevel[target_cls]
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self.name = parent.__name__
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self.propagate = frozenset()
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self.listeners = ()
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def for_modify(self, obj):
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"""Return an event collection which can be modified.
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For _EmptyListener at the instance level of
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a dispatcher, this generates a new
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_ListenerCollection, applies it to the instance,
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and returns it.
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"""
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result = _ListenerCollection(self.parent, obj._parent_cls)
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if obj.__dict__[self.name] is self:
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obj.__dict__[self.name] = result
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return result
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def _needs_modify(self, *args, **kw):
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raise NotImplementedError("need to call for_modify()")
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exec_once = insert = append = remove = clear = _needs_modify
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def __call__(self, *args, **kw):
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"""Execute this event."""
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for fn in self.parent_listeners:
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fn(*args, **kw)
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def __len__(self):
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return len(self.parent_listeners)
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def __iter__(self):
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return iter(self.parent_listeners)
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def __nonzero__(self):
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return bool(self.parent_listeners)
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class _CompoundListener(object):
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_exec_once = False
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def exec_once(self, *args, **kw):
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"""Execute this event, but only if it has not been
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executed already for this collection."""
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if not self._exec_once:
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self(*args, **kw)
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self._exec_once = True
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# I'm not entirely thrilled about the overhead here,
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# but this allows class-level listeners to be added
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# at any point.
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#
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# In the absense of instance-level listeners,
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# we stay with the _EmptyListener object when called
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# at the instance level.
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def __call__(self, *args, **kw):
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"""Execute this event."""
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for fn in self.parent_listeners:
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fn(*args, **kw)
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for fn in self.listeners:
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fn(*args, **kw)
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def __len__(self):
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return len(self.parent_listeners) + len(self.listeners)
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def __iter__(self):
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return chain(self.parent_listeners, self.listeners)
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def __nonzero__(self):
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return bool(self.listeners or self.parent_listeners)
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class _ListenerCollection(_CompoundListener):
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"""Instance-level attributes on instances of :class:`._Dispatch`.
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Represents a collection of listeners.
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As of 0.7.9, _ListenerCollection is only first
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created via the _EmptyListener.for_modify() method.
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"""
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def __init__(self, parent, target_cls):
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if target_cls not in parent._clslevel:
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parent.update_subclass(target_cls)
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self.parent_listeners = parent._clslevel[target_cls]
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self.name = parent.__name__
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self.listeners = []
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self.propagate = set()
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def for_modify(self, obj):
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"""Return an event collection which can be modified.
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For _ListenerCollection at the instance level of
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a dispatcher, this returns self.
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"""
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return self
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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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existing_listeners = self.listeners
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existing_listener_set = set(existing_listeners)
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self.propagate.update(other.propagate)
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existing_listeners.extend([l for l
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in other.listeners
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if l not in existing_listener_set
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and not only_propagate or l in self.propagate
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])
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def insert(self, obj, target, propagate):
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if obj not in self.listeners:
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self.listeners.insert(0, obj)
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if propagate:
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self.propagate.add(obj)
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def append(self, obj, target, propagate):
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if obj not in self.listeners:
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self.listeners.append(obj)
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if propagate:
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self.propagate.add(obj)
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def remove(self, obj, target):
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if obj in self.listeners:
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self.listeners.remove(obj)
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self.propagate.discard(obj)
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def clear(self):
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self.listeners[:] = []
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self.propagate.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 _JoinedDispatchDescriptor(object):
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def __init__(self, name):
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self.name = name
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def __get__(self, obj, cls):
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if obj is None:
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return self
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else:
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obj.__dict__[self.name] = ret = _JoinedListener(
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obj.parent, self.name,
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getattr(obj.local, self.name)
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)
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return ret
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class _JoinedListener(_CompoundListener):
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_exec_once = False
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def __init__(self, parent, name, local):
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self.parent = parent
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self.name = name
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self.local = local
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self.parent_listeners = self.local
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# fix .listeners for the parent. This means
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# new events added to the parent won't be picked
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# up here. Alternatively, the listeners can
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# be via @property to just return getattr(self.parent, self.name)
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# each time. less performant.
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self.listeners = list(getattr(self.parent, self.name))
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def for_modify(self, obj):
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self.local = self.parent_listeners = self.local.for_modify(obj)
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return self
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def insert(self, obj, target, propagate):
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self.local.insert(obj, target, propagate)
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def append(self, obj, target, propagate):
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self.local.append(obj, target, propagate)
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def remove(self, obj, target):
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self.local.remove(obj, target)
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def clear(self):
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raise NotImplementedError()
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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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