1 files changed, 171 insertions, 0 deletions
diff --git a/lib/sqlalchemy/event/base.py b/lib/sqlalchemy/event/base.py
new file mode 100644
index 000000000..bb7b3b1b4
--- /dev/null
+++ b/lib/sqlalchemy/event/base.py
@@ -0,0 +1,171 @@
+"""Base implementation classes.
+
+The public-facing ``Events`` serves as the base class for an event interface;
+it's 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
+
+from .. import util
+from .attr import _JoinedDispatchDescriptor, _EmptyListener, _DispatchDescriptor
+
+_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 _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, self.__class__), {}
+                )
+            for ls in _event_descriptors(self):
+                setattr(cls, ls.name, _JoinedDispatchDescriptor(ls.name))
+
+            self.__class__._joined_dispatch_cls = cls
+        return self._joined_dispatch_cls(self, other)
+
+    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):
+            if isinstance(ls, _EmptyListener):
+                continue
+            getattr(self, ls.name).\
+                for_modify(self)._update(ls, only_propagate=only_propagate)
+
+    @util.hybridmethod
+    def _clear(self):
+        for attr in dir(self):
+            if _is_event_name(attr):
+                getattr(self, attr).for_modify(self).clear()
+
+
+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
+
+    for k in dict_:
+        if _is_event_name(k):
+            setattr(dispatch_cls, k, _DispatchDescriptor(cls, 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(util.with_metaclass(_EventMeta, object)):
+    """Define event listening functions for a particular target type."""
+
+    @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, event_key, propagate=False, insert=False, named=False):
+        event_key.base_listen(propagate=propagate, insert=insert, named=named)
+
+    @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."""
+
+    def __init__(self, local, parent):
+        self.local = local
+        self.parent = parent
+        self._parent_cls = local._parent_cls
+