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diff --git a/lib/sqlalchemy/ext/instrumentation.py b/lib/sqlalchemy/ext/instrumentation.py
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+"""Extensible class instrumentation.
+
+The :mod:`sqlalchemy.ext.instrumentation` package provides for alternate
+systems of class instrumentation within the ORM.  Class instrumentation
+refers to how the ORM places attributes on the class which maintain
+data and track changes to that data, as well as event hooks installed
+on the class.
+
+.. note::
+    The extension package is provided for the benefit of integration
+    with other object management packages, which already perform
+    their own instrumentation.  It is not intended for general use.
+
+For examples of how the instrumentation extension is used,
+see the example :ref:`examples_instrumentation`.
+
+"""
+import weakref
+
+from .. import util
+from ..orm import attributes
+from ..orm import base as orm_base
+from ..orm import collections
+from ..orm import exc as orm_exc
+from ..orm import instrumentation as orm_instrumentation
+from ..orm.instrumentation import _default_dict_getter
+from ..orm.instrumentation import _default_manager_getter
+from ..orm.instrumentation import _default_state_getter
+from ..orm.instrumentation import ClassManager
+from ..orm.instrumentation import InstrumentationFactory
+
+
+INSTRUMENTATION_MANAGER = "__sa_instrumentation_manager__"
+"""Attribute, elects custom instrumentation when present on a mapped class.
+
+Allows a class to specify a slightly or wildly different technique for
+tracking changes made to mapped attributes and collections.
+
+Only one instrumentation implementation is allowed in a given object
+inheritance hierarchy.
+
+The value of this attribute must be a callable and will be passed a class
+object.  The callable must return one of:
+
+  - An instance of an :class:`.InstrumentationManager` or subclass
+  - An object implementing all or some of InstrumentationManager (TODO)
+  - A dictionary of callables, implementing all or some of the above (TODO)
+  - An instance of a :class:`.ClassManager` or subclass
+
+This attribute is consulted by SQLAlchemy instrumentation
+resolution, once the :mod:`sqlalchemy.ext.instrumentation` module
+has been imported.  If custom finders are installed in the global
+instrumentation_finders list, they may or may not choose to honor this
+attribute.
+
+"""
+
+
+def find_native_user_instrumentation_hook(cls):
+    """Find user-specified instrumentation management for a class."""
+    return getattr(cls, INSTRUMENTATION_MANAGER, None)
+
+
+instrumentation_finders = [find_native_user_instrumentation_hook]
+"""An extensible sequence of callables which return instrumentation
+implementations
+
+When a class is registered, each callable will be passed a class object.
+If None is returned, the
+next finder in the sequence is consulted.  Otherwise the return must be an
+instrumentation factory that follows the same guidelines as
+sqlalchemy.ext.instrumentation.INSTRUMENTATION_MANAGER.
+
+By default, the only finder is find_native_user_instrumentation_hook, which
+searches for INSTRUMENTATION_MANAGER.  If all finders return None, standard
+ClassManager instrumentation is used.
+
+"""
+
+
+class ExtendedInstrumentationRegistry(InstrumentationFactory):
+    """Extends :class:`.InstrumentationFactory` with additional
+    bookkeeping, to accommodate multiple types of
+    class managers.
+
+    """
+
+    _manager_finders = weakref.WeakKeyDictionary()
+    _state_finders = weakref.WeakKeyDictionary()
+    _dict_finders = weakref.WeakKeyDictionary()
+    _extended = False
+
+    def _locate_extended_factory(self, class_):
+        for finder in instrumentation_finders:
+            factory = finder(class_)
+            if factory is not None:
+                manager = self._extended_class_manager(class_, factory)
+                return manager, factory
+        else:
+            return None, None
+
+    def _check_conflicts(self, class_, factory):
+        existing_factories = self._collect_management_factories_for(
+            class_
+        ).difference([factory])
+        if existing_factories:
+            raise TypeError(
+                "multiple instrumentation implementations specified "
+                "in %s inheritance hierarchy: %r"
+                % (class_.__name__, list(existing_factories))
+            )
+
+    def _extended_class_manager(self, class_, factory):
+        manager = factory(class_)
+        if not isinstance(manager, ClassManager):
+            manager = _ClassInstrumentationAdapter(class_, manager)
+
+        if factory != ClassManager and not self._extended:
+            # somebody invoked a custom ClassManager.
+            # reinstall global "getter" functions with the more
+            # expensive ones.
+            self._extended = True
+            _install_instrumented_lookups()
+
+        self._manager_finders[class_] = manager.manager_getter()
+        self._state_finders[class_] = manager.state_getter()
+        self._dict_finders[class_] = manager.dict_getter()
+        return manager
+
+    def _collect_management_factories_for(self, cls):
+        """Return a collection of factories in play or specified for a
+        hierarchy.
+
+        Traverses the entire inheritance graph of a cls and returns a
+        collection of instrumentation factories for those classes. Factories
+        are extracted from active ClassManagers, if available, otherwise
+        instrumentation_finders is consulted.
+
+        """
+        hierarchy = util.class_hierarchy(cls)
+        factories = set()
+        for member in hierarchy:
+            manager = self.manager_of_class(member)
+            if manager is not None:
+                factories.add(manager.factory)
+            else:
+                for finder in instrumentation_finders:
+                    factory = finder(member)
+                    if factory is not None:
+                        break
+                else:
+                    factory = None
+                factories.add(factory)
+        factories.discard(None)
+        return factories
+
+    def unregister(self, class_):
+        super(ExtendedInstrumentationRegistry, self).unregister(class_)
+        if class_ in self._manager_finders:
+            del self._manager_finders[class_]
+            del self._state_finders[class_]
+            del self._dict_finders[class_]
+
+    def manager_of_class(self, cls):
+        if cls is None:
+            return None
+        try:
+            finder = self._manager_finders.get(cls, _default_manager_getter)
+        except TypeError:
+            # due to weakref lookup on invalid object
+            return None
+        else:
+            return finder(cls)
+
+    def state_of(self, instance):
+        if instance is None:
+            raise AttributeError("None has no persistent state.")
+        return self._state_finders.get(
+            instance.__class__, _default_state_getter
+        )(instance)
+
+    def dict_of(self, instance):
+        if instance is None:
+            raise AttributeError("None has no persistent state.")
+        return self._dict_finders.get(
+            instance.__class__, _default_dict_getter
+        )(instance)
+
+
+orm_instrumentation._instrumentation_factory = (
+    _instrumentation_factory
+) = ExtendedInstrumentationRegistry()
+orm_instrumentation.instrumentation_finders = instrumentation_finders
+
+
+class InstrumentationManager(object):
+    """User-defined class instrumentation extension.
+
+    :class:`.InstrumentationManager` can be subclassed in order
+    to change
+    how class instrumentation proceeds. This class exists for
+    the purposes of integration with other object management
+    frameworks which would like to entirely modify the
+    instrumentation methodology of the ORM, and is not intended
+    for regular usage.  For interception of class instrumentation
+    events, see :class:`.InstrumentationEvents`.
+
+    The API for this class should be considered as semi-stable,
+    and may change slightly with new releases.
+
+    """
+
+    # r4361 added a mandatory (cls) constructor to this interface.
+    # given that, perhaps class_ should be dropped from all of these
+    # signatures.
+
+    def __init__(self, class_):
+        pass
+
+    def manage(self, class_, manager):
+        setattr(class_, "_default_class_manager", manager)
+
+    def unregister(self, class_, manager):
+        delattr(class_, "_default_class_manager")
+
+    def manager_getter(self, class_):
+        def get(cls):
+            return cls._default_class_manager
+
+        return get
+
+    def instrument_attribute(self, class_, key, inst):
+        pass
+
+    def post_configure_attribute(self, class_, key, inst):
+        pass
+
+    def install_descriptor(self, class_, key, inst):
+        setattr(class_, key, inst)
+
+    def uninstall_descriptor(self, class_, key):
+        delattr(class_, key)
+
+    def install_member(self, class_, key, implementation):
+        setattr(class_, key, implementation)
+
+    def uninstall_member(self, class_, key):
+        delattr(class_, key)
+
+    def instrument_collection_class(self, class_, key, collection_class):
+        return collections.prepare_instrumentation(collection_class)
+
+    def get_instance_dict(self, class_, instance):
+        return instance.__dict__
+
+    def initialize_instance_dict(self, class_, instance):
+        pass
+
+    def install_state(self, class_, instance, state):
+        setattr(instance, "_default_state", state)
+
+    def remove_state(self, class_, instance):
+        delattr(instance, "_default_state")
+
+    def state_getter(self, class_):
+        return lambda instance: getattr(instance, "_default_state")
+
+    def dict_getter(self, class_):
+        return lambda inst: self.get_instance_dict(class_, inst)
+
+
+class _ClassInstrumentationAdapter(ClassManager):
+    """Adapts a user-defined InstrumentationManager to a ClassManager."""
+
+    def __init__(self, class_, override):
+        self._adapted = override
+        self._get_state = self._adapted.state_getter(class_)
+        self._get_dict = self._adapted.dict_getter(class_)
+
+        ClassManager.__init__(self, class_)
+
+    def manage(self):
+        self._adapted.manage(self.class_, self)
+
+    def unregister(self):
+        self._adapted.unregister(self.class_, self)
+
+    def manager_getter(self):
+        return self._adapted.manager_getter(self.class_)
+
+    def instrument_attribute(self, key, inst, propagated=False):
+        ClassManager.instrument_attribute(self, key, inst, propagated)
+        if not propagated:
+            self._adapted.instrument_attribute(self.class_, key, inst)
+
+    def post_configure_attribute(self, key):
+        super(_ClassInstrumentationAdapter, self).post_configure_attribute(key)
+        self._adapted.post_configure_attribute(self.class_, key, self[key])
+
+    def install_descriptor(self, key, inst):
+        self._adapted.install_descriptor(self.class_, key, inst)
+
+    def uninstall_descriptor(self, key):
+        self._adapted.uninstall_descriptor(self.class_, key)
+
+    def install_member(self, key, implementation):
+        self._adapted.install_member(self.class_, key, implementation)
+
+    def uninstall_member(self, key):
+        self._adapted.uninstall_member(self.class_, key)
+
+    def instrument_collection_class(self, key, collection_class):
+        return self._adapted.instrument_collection_class(
+            self.class_, key, collection_class
+        )
+
+    def initialize_collection(self, key, state, factory):
+        delegate = getattr(self._adapted, "initialize_collection", None)
+        if delegate:
+            return delegate(key, state, factory)
+        else:
+            return ClassManager.initialize_collection(
+                self, key, state, factory
+            )
+
+    def new_instance(self, state=None):
+        instance = self.class_.__new__(self.class_)
+        self.setup_instance(instance, state)
+        return instance
+
+    def _new_state_if_none(self, instance):
+        """Install a default InstanceState if none is present.
+
+        A private convenience method used by the __init__ decorator.
+        """
+        if self.has_state(instance):
+            return False
+        else:
+            return self.setup_instance(instance)
+
+    def setup_instance(self, instance, state=None):
+        self._adapted.initialize_instance_dict(self.class_, instance)
+
+        if state is None:
+            state = self._state_constructor(instance, self)
+
+        # the given instance is assumed to have no state
+        self._adapted.install_state(self.class_, instance, state)
+        return state
+
+    def teardown_instance(self, instance):
+        self._adapted.remove_state(self.class_, instance)
+
+    def has_state(self, instance):
+        try:
+            self._get_state(instance)
+        except orm_exc.NO_STATE:
+            return False
+        else:
+            return True
+
+    def state_getter(self):
+        return self._get_state
+
+    def dict_getter(self):
+        return self._get_dict
+
+
+def _install_instrumented_lookups():
+    """Replace global class/object management functions
+    with ExtendedInstrumentationRegistry implementations, which
+    allow multiple types of class managers to be present,
+    at the cost of performance.
+
+    This function is called only by ExtendedInstrumentationRegistry
+    and unit tests specific to this behavior.
+
+    The _reinstall_default_lookups() function can be called
+    after this one to re-establish the default functions.
+
+    """
+    _install_lookups(
+        dict(
+            instance_state=_instrumentation_factory.state_of,
+            instance_dict=_instrumentation_factory.dict_of,
+            manager_of_class=_instrumentation_factory.manager_of_class,
+        )
+    )
+
+
+def _reinstall_default_lookups():
+    """Restore simplified lookups."""
+    _install_lookups(
+        dict(
+            instance_state=_default_state_getter,
+            instance_dict=_default_dict_getter,
+            manager_of_class=_default_manager_getter,
+        )
+    )
+    _instrumentation_factory._extended = False
+
+
+def _install_lookups(lookups):
+    global instance_state, instance_dict, manager_of_class
+    instance_state = lookups["instance_state"]
+    instance_dict = lookups["instance_dict"]
+    manager_of_class = lookups["manager_of_class"]
+    orm_base.instance_state = (
+        attributes.instance_state
+    ) = orm_instrumentation.instance_state = instance_state
+    orm_base.instance_dict = (
+        attributes.instance_dict
+    ) = orm_instrumentation.instance_dict = instance_dict
+    orm_base.manager_of_class = (
+        attributes.manager_of_class
+    ) = orm_instrumentation.manager_of_class = manager_of_class