Initial Configuration Push

deps/sqlalchemy/event/base.py

@@ -0,0 +1,289 @@
+# event/base.py
+# Copyright (C) 2005-2016 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 .. import util
+from .attr import _JoinedListener, \
+    _EmptyListener, _ClsLevelDispatch
+
+_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, _instance_cls):
+        for cls in _instance_cls.__mro__:
+            if 'dispatch' in cls.__dict__:
+                return cls.__dict__['dispatch'].\
+                    dispatch_cls._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] = dict(
+                        (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 getattr(self, k)
+
+    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)
+
+    @property
+    def _listen(self):
+        return self._events._listen
+
+    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_)
+        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.
+    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):
+        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>"
+        # @staticemethod 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):
+        # Mapper, ClassManager, Session override this to
+        # also accept classes, scoped_sessions, sessionmakers, etc.
+        if hasattr(target, 'dispatch') and (
+
+                isinstance(target.dispatch, cls.dispatch.__class__) or
+
+
+                (
+                    isinstance(target.dispatch, type) and
+                    isinstance(target.dispatch, cls.dispatch.__class__)
+                ) or
+
+                (
+                    isinstance(target.dispatch, _JoinedDispatcher) and
+                    isinstance(target.dispatch.parent, cls.dispatch.__class__)
+                )
+
+
+        ):
+            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."""
+
+    __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
+
+
+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._for_instance(obj)
+        return disp