346 lines
11 KiB
Python
346 lines
11 KiB
Python
# event/base.py
|
|
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
|
|
# <see AUTHORS file>
|
|
#
|
|
# This module is part of SQLAlchemy and is released under
|
|
# the MIT License: http://www.opensource.org/licenses/mit-license.php
|
|
|
|
"""Base implementation classes.
|
|
|
|
The public-facing ``Events`` serves as the base class for an event interface;
|
|
its public attributes represent different kinds of events. These attributes
|
|
are mirrored onto a ``_Dispatch`` class, which serves as a container for
|
|
collections of listener functions. These collections are represented both
|
|
at the class level of a particular ``_Dispatch`` class as well as within
|
|
instances of ``_Dispatch``.
|
|
|
|
"""
|
|
from __future__ import absolute_import
|
|
|
|
import weakref
|
|
|
|
from .attr import _ClsLevelDispatch
|
|
from .attr import _EmptyListener
|
|
from .attr import _JoinedListener
|
|
from .. import util
|
|
|
|
|
|
_registrars = util.defaultdict(list)
|
|
|
|
|
|
def _is_event_name(name):
|
|
# _sa_event prefix is special to support internal-only event names.
|
|
# most event names are just plain method names that aren't
|
|
# underscored.
|
|
|
|
return (
|
|
not name.startswith("_") and name != "dispatch"
|
|
) or name.startswith("_sa_event")
|
|
|
|
|
|
class _UnpickleDispatch(object):
|
|
"""Serializable callable that re-generates an instance of
|
|
:class:`_Dispatch` given a particular :class:`.Events` subclass.
|
|
|
|
"""
|
|
|
|
def __call__(self, _instance_cls):
|
|
for cls in _instance_cls.__mro__:
|
|
if "dispatch" in cls.__dict__:
|
|
return cls.__dict__["dispatch"].dispatch._for_class(
|
|
_instance_cls
|
|
)
|
|
else:
|
|
raise AttributeError("No class with a 'dispatch' member present.")
|
|
|
|
|
|
class _Dispatch(object):
|
|
"""Mirror the event listening definitions of an Events class with
|
|
listener collections.
|
|
|
|
Classes which define a "dispatch" member will return a
|
|
non-instantiated :class:`._Dispatch` subclass when the member
|
|
is accessed at the class level. When the "dispatch" member is
|
|
accessed at the instance level of its owner, an instance
|
|
of the :class:`._Dispatch` class is returned.
|
|
|
|
A :class:`._Dispatch` class is generated for each :class:`.Events`
|
|
class defined, by the :func:`._create_dispatcher_class` function.
|
|
The original :class:`.Events` classes remain untouched.
|
|
This decouples the construction of :class:`.Events` subclasses from
|
|
the implementation used by the event internals, and allows
|
|
inspecting tools like Sphinx to work in an unsurprising
|
|
way against the public API.
|
|
|
|
"""
|
|
|
|
# In one ORM edge case, an attribute is added to _Dispatch,
|
|
# so __dict__ is used in just that case and potentially others.
|
|
__slots__ = "_parent", "_instance_cls", "__dict__", "_empty_listeners"
|
|
|
|
_empty_listener_reg = weakref.WeakKeyDictionary()
|
|
|
|
def __init__(self, parent, instance_cls=None):
|
|
self._parent = parent
|
|
self._instance_cls = instance_cls
|
|
|
|
if instance_cls:
|
|
try:
|
|
self._empty_listeners = self._empty_listener_reg[instance_cls]
|
|
except KeyError:
|
|
self._empty_listeners = self._empty_listener_reg[
|
|
instance_cls
|
|
] = {
|
|
ls.name: _EmptyListener(ls, instance_cls)
|
|
for ls in parent._event_descriptors
|
|
}
|
|
else:
|
|
self._empty_listeners = {}
|
|
|
|
def __getattr__(self, name):
|
|
# Assign EmptyListeners as attributes on demand
|
|
# to reduce startup time for new dispatch objects.
|
|
try:
|
|
ls = self._empty_listeners[name]
|
|
except KeyError:
|
|
raise AttributeError(name)
|
|
else:
|
|
setattr(self, ls.name, ls)
|
|
return ls
|
|
|
|
@property
|
|
def _event_descriptors(self):
|
|
for k in self._event_names:
|
|
# Yield _ClsLevelDispatch related
|
|
# to relevant event name.
|
|
yield getattr(self, k)
|
|
|
|
@property
|
|
def _listen(self):
|
|
return self._events._listen
|
|
|
|
def _for_class(self, instance_cls):
|
|
return self.__class__(self, instance_cls)
|
|
|
|
def _for_instance(self, instance):
|
|
instance_cls = instance.__class__
|
|
return self._for_class(instance_cls)
|
|
|
|
def _join(self, other):
|
|
"""Create a 'join' of this :class:`._Dispatch` and another.
|
|
|
|
This new dispatcher will dispatch events to both
|
|
:class:`._Dispatch` objects.
|
|
|
|
"""
|
|
if "_joined_dispatch_cls" not in self.__class__.__dict__:
|
|
cls = type(
|
|
"Joined%s" % self.__class__.__name__,
|
|
(_JoinedDispatcher,),
|
|
{"__slots__": self._event_names},
|
|
)
|
|
|
|
self.__class__._joined_dispatch_cls = cls
|
|
return self._joined_dispatch_cls(self, other)
|
|
|
|
def __reduce__(self):
|
|
return _UnpickleDispatch(), (self._instance_cls,)
|
|
|
|
def _update(self, other, only_propagate=True):
|
|
"""Populate from the listeners in another :class:`_Dispatch`
|
|
object."""
|
|
for ls in other._event_descriptors:
|
|
if isinstance(ls, _EmptyListener):
|
|
continue
|
|
getattr(self, ls.name).for_modify(self)._update(
|
|
ls, only_propagate=only_propagate
|
|
)
|
|
|
|
def _clear(self):
|
|
for ls in self._event_descriptors:
|
|
ls.for_modify(self).clear()
|
|
|
|
|
|
class _EventMeta(type):
|
|
"""Intercept new Event subclasses and create
|
|
associated _Dispatch classes."""
|
|
|
|
def __init__(cls, classname, bases, dict_):
|
|
_create_dispatcher_class(cls, classname, bases, dict_)
|
|
type.__init__(cls, classname, bases, dict_)
|
|
|
|
|
|
def _create_dispatcher_class(cls, classname, bases, dict_):
|
|
"""Create a :class:`._Dispatch` class corresponding to an
|
|
:class:`.Events` class."""
|
|
|
|
# there's all kinds of ways to do this,
|
|
# i.e. make a Dispatch class that shares the '_listen' method
|
|
# of the Event class, this is the straight monkeypatch.
|
|
if hasattr(cls, "dispatch"):
|
|
dispatch_base = cls.dispatch.__class__
|
|
else:
|
|
dispatch_base = _Dispatch
|
|
|
|
event_names = [k for k in dict_ if _is_event_name(k)]
|
|
dispatch_cls = type(
|
|
"%sDispatch" % classname, (dispatch_base,), {"__slots__": event_names}
|
|
)
|
|
|
|
dispatch_cls._event_names = event_names
|
|
|
|
dispatch_inst = cls._set_dispatch(cls, dispatch_cls)
|
|
for k in dispatch_cls._event_names:
|
|
setattr(dispatch_inst, k, _ClsLevelDispatch(cls, dict_[k]))
|
|
_registrars[k].append(cls)
|
|
|
|
for super_ in dispatch_cls.__bases__:
|
|
if issubclass(super_, _Dispatch) and super_ is not _Dispatch:
|
|
for ls in super_._events.dispatch._event_descriptors:
|
|
setattr(dispatch_inst, ls.name, ls)
|
|
dispatch_cls._event_names.append(ls.name)
|
|
|
|
if getattr(cls, "_dispatch_target", None):
|
|
the_cls = cls._dispatch_target
|
|
if (
|
|
hasattr(the_cls, "__slots__")
|
|
and "_slots_dispatch" in the_cls.__slots__
|
|
):
|
|
cls._dispatch_target.dispatch = slots_dispatcher(cls)
|
|
else:
|
|
cls._dispatch_target.dispatch = dispatcher(cls)
|
|
|
|
|
|
def _remove_dispatcher(cls):
|
|
for k in cls.dispatch._event_names:
|
|
_registrars[k].remove(cls)
|
|
if not _registrars[k]:
|
|
del _registrars[k]
|
|
|
|
|
|
class Events(util.with_metaclass(_EventMeta, object)):
|
|
"""Define event listening functions for a particular target type."""
|
|
|
|
@staticmethod
|
|
def _set_dispatch(cls, dispatch_cls):
|
|
# This allows an Events subclass to define additional utility
|
|
# methods made available to the target via
|
|
# "self.dispatch._events.<utilitymethod>"
|
|
# @staticmethod to allow easy "super" calls while in a metaclass
|
|
# constructor.
|
|
cls.dispatch = dispatch_cls(None)
|
|
dispatch_cls._events = cls
|
|
return cls.dispatch
|
|
|
|
@classmethod
|
|
def _accept_with(cls, target):
|
|
def dispatch_is(*types):
|
|
return all(isinstance(target.dispatch, t) for t in types)
|
|
|
|
def dispatch_parent_is(t):
|
|
return isinstance(target.dispatch.parent, t)
|
|
|
|
# Mapper, ClassManager, Session override this to
|
|
# also accept classes, scoped_sessions, sessionmakers, etc.
|
|
if hasattr(target, "dispatch"):
|
|
if (
|
|
dispatch_is(cls.dispatch.__class__)
|
|
or dispatch_is(type, cls.dispatch.__class__)
|
|
or (
|
|
dispatch_is(_JoinedDispatcher)
|
|
and dispatch_parent_is(cls.dispatch.__class__)
|
|
)
|
|
):
|
|
return target
|
|
|
|
@classmethod
|
|
def _listen(
|
|
cls,
|
|
event_key,
|
|
propagate=False,
|
|
insert=False,
|
|
named=False,
|
|
asyncio=False,
|
|
):
|
|
event_key.base_listen(
|
|
propagate=propagate, insert=insert, named=named, asyncio=asyncio
|
|
)
|
|
|
|
@classmethod
|
|
def _remove(cls, event_key):
|
|
event_key.remove()
|
|
|
|
@classmethod
|
|
def _clear(cls):
|
|
cls.dispatch._clear()
|
|
|
|
|
|
class _JoinedDispatcher(object):
|
|
"""Represent a connection between two _Dispatch objects."""
|
|
|
|
__slots__ = "local", "parent", "_instance_cls"
|
|
|
|
def __init__(self, local, parent):
|
|
self.local = local
|
|
self.parent = parent
|
|
self._instance_cls = self.local._instance_cls
|
|
|
|
def __getattr__(self, name):
|
|
# Assign _JoinedListeners as attributes on demand
|
|
# to reduce startup time for new dispatch objects.
|
|
ls = getattr(self.local, name)
|
|
jl = _JoinedListener(self.parent, ls.name, ls)
|
|
setattr(self, ls.name, jl)
|
|
return jl
|
|
|
|
@property
|
|
def _listen(self):
|
|
return self.parent._listen
|
|
|
|
@property
|
|
def _events(self):
|
|
return self.parent._events
|
|
|
|
|
|
class dispatcher(object):
|
|
"""Descriptor used by target classes to
|
|
deliver the _Dispatch class at the class level
|
|
and produce new _Dispatch instances for target
|
|
instances.
|
|
|
|
"""
|
|
|
|
def __init__(self, events):
|
|
self.dispatch = events.dispatch
|
|
self.events = events
|
|
|
|
def __get__(self, obj, cls):
|
|
if obj is None:
|
|
return self.dispatch
|
|
|
|
disp = self.dispatch._for_instance(obj)
|
|
try:
|
|
obj.__dict__["dispatch"] = disp
|
|
except AttributeError as ae:
|
|
util.raise_(
|
|
TypeError(
|
|
"target %r doesn't have __dict__, should it be "
|
|
"defining _slots_dispatch?" % (obj,)
|
|
),
|
|
replace_context=ae,
|
|
)
|
|
return disp
|
|
|
|
|
|
class slots_dispatcher(dispatcher):
|
|
def __get__(self, obj, cls):
|
|
if obj is None:
|
|
return self.dispatch
|
|
|
|
if hasattr(obj, "_slots_dispatch"):
|
|
return obj._slots_dispatch
|
|
|
|
disp = self.dispatch._for_instance(obj)
|
|
obj._slots_dispatch = disp
|
|
return disp
|