/usr/share/pyshared/sqlalchemy/event.py is in python-sqlalchemy 0.7.4-1.
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# Copyright (C) 2005-2011 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 event API."""
from sqlalchemy import util, exc
CANCEL = util.symbol('CANCEL')
NO_RETVAL = util.symbol('NO_RETVAL')
def listen(target, identifier, fn, *args, **kw):
"""Register a listener function for the given target.
e.g.::
from sqlalchemy import event
from sqlalchemy.schema import UniqueConstraint
def unique_constraint_name(const, table):
const.name = "uq_%s_%s" % (
table.name,
list(const.columns)[0].name
)
event.listen(
UniqueConstraint,
"after_parent_attach",
unique_constraint_name)
"""
for evt_cls in _registrars[identifier]:
tgt = evt_cls._accept_with(target)
if tgt is not None:
tgt.dispatch._listen(tgt, identifier, fn, *args, **kw)
return
raise exc.InvalidRequestError("No such event '%s' for target '%s'" %
(identifier,target))
def listens_for(target, identifier, *args, **kw):
"""Decorate a function as a listener for the given target + identifier.
e.g.::
from sqlalchemy import event
from sqlalchemy.schema import UniqueConstraint
@event.listens_for(UniqueConstraint, "after_parent_attach")
def unique_constraint_name(const, table):
const.name = "uq_%s_%s" % (
table.name,
list(const.columns)[0].name
)
"""
def decorate(fn):
listen(target, identifier, fn, *args, **kw)
return fn
return decorate
def remove(target, identifier, fn):
"""Remove an event listener.
Note that some event removals, particularly for those event dispatchers
which create wrapper functions and secondary even listeners, may not yet
be supported.
"""
for evt_cls in _registrars[identifier]:
for tgt in evt_cls._accept_with(target):
tgt.dispatch._remove(identifier, tgt, fn, *args, **kw)
return
_registrars = util.defaultdict(list)
def _is_event_name(name):
return not name.startswith('_') and name != 'dispatch'
class _UnpickleDispatch(object):
"""Serializable callable that re-generates an instance of :class:`_Dispatch`
given a particular :class:`.Events` subclass.
"""
def __call__(self, _parent_cls):
for cls in _parent_cls.__mro__:
if 'dispatch' in cls.__dict__:
return cls.__dict__['dispatch'].dispatch_cls(_parent_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.
"""
def __init__(self, _parent_cls):
self._parent_cls = _parent_cls
def __reduce__(self):
return _UnpickleDispatch(), (self._parent_cls, )
def _update(self, other, only_propagate=True):
"""Populate from the listeners in another :class:`_Dispatch`
object."""
for ls in _event_descriptors(other):
getattr(self, ls.name)._update(ls, only_propagate=only_propagate)
def _event_descriptors(target):
return [getattr(target, k) for k in dir(target) if _is_event_name(k)]
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_)
return 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.
dispatch_base = getattr(cls, 'dispatch', _Dispatch)
cls.dispatch = dispatch_cls = type("%sDispatch" % classname,
(dispatch_base, ), {})
dispatch_cls._listen = cls._listen
dispatch_cls._clear = cls._clear
for k in dict_:
if _is_event_name(k):
setattr(dispatch_cls, k, _DispatchDescriptor(dict_[k]))
_registrars[k].append(cls)
def _remove_dispatcher(cls):
for k in dir(cls):
if _is_event_name(k):
_registrars[k].remove(cls)
if not _registrars[k]:
del _registrars[k]
class Events(object):
"""Define event listening functions for a particular target type."""
__metaclass__ = _EventMeta
@classmethod
def _accept_with(cls, target):
# Mapper, ClassManager, Session override this to
# also accept classes, scoped_sessions, sessionmakers, etc.
if hasattr(target, 'dispatch') and (
isinstance(target.dispatch, cls.dispatch) or \
isinstance(target.dispatch, type) and \
issubclass(target.dispatch, cls.dispatch)
):
return target
else:
return None
@classmethod
def _listen(cls, target, identifier, fn, propagate=False, insert=False):
if insert:
getattr(target.dispatch, identifier).insert(fn, target, propagate)
else:
getattr(target.dispatch, identifier).append(fn, target, propagate)
@classmethod
def _remove(cls, target, identifier, fn):
getattr(target.dispatch, identifier).remove(fn, target)
@classmethod
def _clear(cls):
for attr in dir(cls.dispatch):
if _is_event_name(attr):
getattr(cls.dispatch, attr).clear()
class _DispatchDescriptor(object):
"""Class-level attributes on :class:`._Dispatch` classes."""
def __init__(self, fn):
self.__name__ = fn.__name__
self.__doc__ = fn.__doc__
self._clslevel = util.defaultdict(list)
def insert(self, obj, target, propagate):
assert isinstance(target, type), \
"Class-level Event targets must be classes."
stack = [target]
while stack:
cls = stack.pop(0)
stack.extend(cls.__subclasses__())
self._clslevel[cls].insert(0, obj)
def append(self, obj, target, propagate):
assert isinstance(target, type), \
"Class-level Event targets must be classes."
stack = [target]
while stack:
cls = stack.pop(0)
stack.extend(cls.__subclasses__())
self._clslevel[cls].append(obj)
def remove(self, obj, target):
stack = [target]
while stack:
cls = stack.pop(0)
stack.extend(cls.__subclasses__())
self._clslevel[cls].remove(obj)
def clear(self):
"""Clear all class level listeners"""
for dispatcher in self._clslevel.values():
dispatcher[:] = []
def __get__(self, obj, cls):
if obj is None:
return self
obj.__dict__[self.__name__] = result = \
_ListenerCollection(self, obj._parent_cls)
return result
class _ListenerCollection(object):
"""Instance-level attributes on instances of :class:`._Dispatch`.
Represents a collection of listeners.
"""
_exec_once = False
def __init__(self, parent, target_cls):
self.parent_listeners = parent._clslevel[target_cls]
self.name = parent.__name__
self.listeners = []
self.propagate = set()
def exec_once(self, *args, **kw):
"""Execute this event, but only if it has not been
executed already for this collection."""
if not self._exec_once:
self(*args, **kw)
self._exec_once = True
def __call__(self, *args, **kw):
"""Execute this event."""
for fn in self.parent_listeners:
fn(*args, **kw)
for fn in self.listeners:
fn(*args, **kw)
# I'm not entirely thrilled about the overhead here,
# but this allows class-level listeners to be added
# at any point.
#
# alternatively, _DispatchDescriptor could notify
# all _ListenerCollection objects, but then we move
# to a higher memory model, i.e.weakrefs to all _ListenerCollection
# objects, the _DispatchDescriptor collection repeated
# for all instances.
def __len__(self):
return len(self.parent_listeners + self.listeners)
def __iter__(self):
return iter(self.parent_listeners + self.listeners)
def __getitem__(self, index):
return (self.parent_listeners + self.listeners)[index]
def __nonzero__(self):
return bool(self.listeners or self.parent_listeners)
def _update(self, other, only_propagate=True):
"""Populate from the listeners in another :class:`_Dispatch`
object."""
existing_listeners = self.listeners
existing_listener_set = set(existing_listeners)
self.propagate.update(other.propagate)
existing_listeners.extend([l for l
in other.listeners
if l not in existing_listener_set
and not only_propagate or l in self.propagate
])
def insert(self, obj, target, propagate):
if obj not in self.listeners:
self.listeners.insert(0, obj)
if propagate:
self.propagate.add(obj)
def append(self, obj, target, propagate):
if obj not in self.listeners:
self.listeners.append(obj)
if propagate:
self.propagate.add(obj)
def remove(self, obj, target):
if obj in self.listeners:
self.listeners.remove(obj)
self.propagate.discard(obj)
def clear(self):
self.listeners[:] = []
self.propagate.clear()
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_cls = events.dispatch
self.events = events
def __get__(self, obj, cls):
if obj is None:
return self.dispatch_cls
obj.__dict__['dispatch'] = disp = self.dispatch_cls(cls)
return disp
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