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+# ext/mutable.py
+# Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
+# <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: https://www.opensource.org/licenses/mit-license.php
+
+r"""Provide support for tracking of in-place changes to scalar values,
+which are propagated into ORM change events on owning parent objects.
+
+.. _mutable_scalars:
+
+Establishing Mutability on Scalar Column Values
+===============================================
+
+A typical example of a "mutable" structure is a Python dictionary.
+Following the example introduced in :ref:`types_toplevel`, we
+begin with a custom type that marshals Python dictionaries into
+JSON strings before being persisted::
+
+    from sqlalchemy.types import TypeDecorator, VARCHAR
+    import json
+
+    class JSONEncodedDict(TypeDecorator):
+        "Represents an immutable structure as a json-encoded string."
+
+        impl = VARCHAR
+
+        def process_bind_param(self, value, dialect):
+            if value is not None:
+                value = json.dumps(value)
+            return value
+
+        def process_result_value(self, value, dialect):
+            if value is not None:
+                value = json.loads(value)
+            return value
+
+The usage of ``json`` is only for the purposes of example. The
+:mod:`sqlalchemy.ext.mutable` extension can be used
+with any type whose target Python type may be mutable, including
+:class:`.PickleType`, :class:`_postgresql.ARRAY`, etc.
+
+When using the :mod:`sqlalchemy.ext.mutable` extension, the value itself
+tracks all parents which reference it.  Below, we illustrate a simple
+version of the :class:`.MutableDict` dictionary object, which applies
+the :class:`.Mutable` mixin to a plain Python dictionary::
+
+    from sqlalchemy.ext.mutable import Mutable
+
+    class MutableDict(Mutable, dict):
+        @classmethod
+        def coerce(cls, key, value):
+            "Convert plain dictionaries to MutableDict."
+
+            if not isinstance(value, MutableDict):
+                if isinstance(value, dict):
+                    return MutableDict(value)
+
+                # this call will raise ValueError
+                return Mutable.coerce(key, value)
+            else:
+                return value
+
+        def __setitem__(self, key, value):
+            "Detect dictionary set events and emit change events."
+
+            dict.__setitem__(self, key, value)
+            self.changed()
+
+        def __delitem__(self, key):
+            "Detect dictionary del events and emit change events."
+
+            dict.__delitem__(self, key)
+            self.changed()
+
+The above dictionary class takes the approach of subclassing the Python
+built-in ``dict`` to produce a dict
+subclass which routes all mutation events through ``__setitem__``.  There are
+variants on this approach, such as subclassing ``UserDict.UserDict`` or
+``collections.MutableMapping``; the part that's important to this example is
+that the :meth:`.Mutable.changed` method is called whenever an in-place
+change to the datastructure takes place.
+
+We also redefine the :meth:`.Mutable.coerce` method which will be used to
+convert any values that are not instances of ``MutableDict``, such
+as the plain dictionaries returned by the ``json`` module, into the
+appropriate type.  Defining this method is optional; we could just as well
+created our ``JSONEncodedDict`` such that it always returns an instance
+of ``MutableDict``, and additionally ensured that all calling code
+uses ``MutableDict`` explicitly.  When :meth:`.Mutable.coerce` is not
+overridden, any values applied to a parent object which are not instances
+of the mutable type will raise a ``ValueError``.
+
+Our new ``MutableDict`` type offers a class method
+:meth:`~.Mutable.as_mutable` which we can use within column metadata
+to associate with types. This method grabs the given type object or
+class and associates a listener that will detect all future mappings
+of this type, applying event listening instrumentation to the mapped
+attribute. Such as, with classical table metadata::
+
+    from sqlalchemy import Table, Column, Integer
+
+    my_data = Table('my_data', metadata,
+        Column('id', Integer, primary_key=True),
+        Column('data', MutableDict.as_mutable(JSONEncodedDict))
+    )
+
+Above, :meth:`~.Mutable.as_mutable` returns an instance of ``JSONEncodedDict``
+(if the type object was not an instance already), which will intercept any
+attributes which are mapped against this type.  Below we establish a simple
+mapping against the ``my_data`` table::
+
+    from sqlalchemy import mapper
+
+    class MyDataClass(object):
+        pass
+
+    # associates mutation listeners with MyDataClass.data
+    mapper(MyDataClass, my_data)
+
+The ``MyDataClass.data`` member will now be notified of in place changes
+to its value.
+
+There's no difference in usage when using declarative::
+
+    from sqlalchemy.ext.declarative import declarative_base
+
+    Base = declarative_base()
+
+    class MyDataClass(Base):
+        __tablename__ = 'my_data'
+        id = Column(Integer, primary_key=True)
+        data = Column(MutableDict.as_mutable(JSONEncodedDict))
+
+Any in-place changes to the ``MyDataClass.data`` member
+will flag the attribute as "dirty" on the parent object::
+
+    >>> from sqlalchemy.orm import Session
+
+    >>> sess = Session()
+    >>> m1 = MyDataClass(data={'value1':'foo'})
+    >>> sess.add(m1)
+    >>> sess.commit()
+
+    >>> m1.data['value1'] = 'bar'
+    >>> assert m1 in sess.dirty
+    True
+
+The ``MutableDict`` can be associated with all future instances
+of ``JSONEncodedDict`` in one step, using
+:meth:`~.Mutable.associate_with`.  This is similar to
+:meth:`~.Mutable.as_mutable` except it will intercept all occurrences
+of ``MutableDict`` in all mappings unconditionally, without
+the need to declare it individually::
+
+    MutableDict.associate_with(JSONEncodedDict)
+
+    class MyDataClass(Base):
+        __tablename__ = 'my_data'
+        id = Column(Integer, primary_key=True)
+        data = Column(JSONEncodedDict)
+
+
+Supporting Pickling
+--------------------
+
+The key to the :mod:`sqlalchemy.ext.mutable` extension relies upon the
+placement of a ``weakref.WeakKeyDictionary`` upon the value object, which
+stores a mapping of parent mapped objects keyed to the attribute name under
+which they are associated with this value. ``WeakKeyDictionary`` objects are
+not picklable, due to the fact that they contain weakrefs and function
+callbacks. In our case, this is a good thing, since if this dictionary were
+picklable, it could lead to an excessively large pickle size for our value
+objects that are pickled by themselves outside of the context of the parent.
+The developer responsibility here is only to provide a ``__getstate__`` method
+that excludes the :meth:`~MutableBase._parents` collection from the pickle
+stream::
+
+    class MyMutableType(Mutable):
+        def __getstate__(self):
+            d = self.__dict__.copy()
+            d.pop('_parents', None)
+            return d
+
+With our dictionary example, we need to return the contents of the dict itself
+(and also restore them on __setstate__)::
+
+    class MutableDict(Mutable, dict):
+        # ....
+
+        def __getstate__(self):
+            return dict(self)
+
+        def __setstate__(self, state):
+            self.update(state)
+
+In the case that our mutable value object is pickled as it is attached to one
+or more parent objects that are also part of the pickle, the :class:`.Mutable`
+mixin will re-establish the :attr:`.Mutable._parents` collection on each value
+object as the owning parents themselves are unpickled.
+
+Receiving Events
+----------------
+
+The :meth:`.AttributeEvents.modified` event handler may be used to receive
+an event when a mutable scalar emits a change event.  This event handler
+is called when the :func:`.attributes.flag_modified` function is called
+from within the mutable extension::
+
+    from sqlalchemy.ext.declarative import declarative_base
+    from sqlalchemy import event
+
+    Base = declarative_base()
+
+    class MyDataClass(Base):
+        __tablename__ = 'my_data'
+        id = Column(Integer, primary_key=True)
+        data = Column(MutableDict.as_mutable(JSONEncodedDict))
+
+    @event.listens_for(MyDataClass.data, "modified")
+    def modified_json(instance):
+        print("json value modified:", instance.data)
+
+.. _mutable_composites:
+
+Establishing Mutability on Composites
+=====================================
+
+Composites are a special ORM feature which allow a single scalar attribute to
+be assigned an object value which represents information "composed" from one
+or more columns from the underlying mapped table. The usual example is that of
+a geometric "point", and is introduced in :ref:`mapper_composite`.
+
+As is the case with :class:`.Mutable`, the user-defined composite class
+subclasses :class:`.MutableComposite` as a mixin, and detects and delivers
+change events to its parents via the :meth:`.MutableComposite.changed` method.
+In the case of a composite class, the detection is usually via the usage of
+Python descriptors (i.e. ``@property``), or alternatively via the special
+Python method ``__setattr__()``. Below we expand upon the ``Point`` class
+introduced in :ref:`mapper_composite` to subclass :class:`.MutableComposite`
+and to also route attribute set events via ``__setattr__`` to the
+:meth:`.MutableComposite.changed` method::
+
+    from sqlalchemy.ext.mutable import MutableComposite
+
+    class Point(MutableComposite):
+        def __init__(self, x, y):
+            self.x = x
+            self.y = y
+
+        def __setattr__(self, key, value):
+            "Intercept set events"
+
+            # set the attribute
+            object.__setattr__(self, key, value)
+
+            # alert all parents to the change
+            self.changed()
+
+        def __composite_values__(self):
+            return self.x, self.y
+
+        def __eq__(self, other):
+            return isinstance(other, Point) and \
+                other.x == self.x and \
+                other.y == self.y
+
+        def __ne__(self, other):
+            return not self.__eq__(other)
+
+The :class:`.MutableComposite` class uses a Python metaclass to automatically
+establish listeners for any usage of :func:`_orm.composite` that specifies our
+``Point`` type. Below, when ``Point`` is mapped to the ``Vertex`` class,
+listeners are established which will route change events from ``Point``
+objects to each of the ``Vertex.start`` and ``Vertex.end`` attributes::
+
+    from sqlalchemy.orm import composite, mapper
+    from sqlalchemy import Table, Column
+
+    vertices = Table('vertices', metadata,
+        Column('id', Integer, primary_key=True),
+        Column('x1', Integer),
+        Column('y1', Integer),
+        Column('x2', Integer),
+        Column('y2', Integer),
+        )
+
+    class Vertex(object):
+        pass
+
+    mapper(Vertex, vertices, properties={
+        'start': composite(Point, vertices.c.x1, vertices.c.y1),
+        'end': composite(Point, vertices.c.x2, vertices.c.y2)
+    })
+
+Any in-place changes to the ``Vertex.start`` or ``Vertex.end`` members
+will flag the attribute as "dirty" on the parent object::
+
+    >>> from sqlalchemy.orm import Session
+
+    >>> sess = Session()
+    >>> v1 = Vertex(start=Point(3, 4), end=Point(12, 15))
+    >>> sess.add(v1)
+    >>> sess.commit()
+
+    >>> v1.end.x = 8
+    >>> assert v1 in sess.dirty
+    True
+
+Coercing Mutable Composites
+---------------------------
+
+The :meth:`.MutableBase.coerce` method is also supported on composite types.
+In the case of :class:`.MutableComposite`, the :meth:`.MutableBase.coerce`
+method is only called for attribute set operations, not load operations.
+Overriding the :meth:`.MutableBase.coerce` method is essentially equivalent
+to using a :func:`.validates` validation routine for all attributes which
+make use of the custom composite type::
+
+    class Point(MutableComposite):
+        # other Point methods
+        # ...
+
+        def coerce(cls, key, value):
+            if isinstance(value, tuple):
+                value = Point(*value)
+            elif not isinstance(value, Point):
+                raise ValueError("tuple or Point expected")
+            return value
+
+Supporting Pickling
+--------------------
+
+As is the case with :class:`.Mutable`, the :class:`.MutableComposite` helper
+class uses a ``weakref.WeakKeyDictionary`` available via the
+:meth:`MutableBase._parents` attribute which isn't picklable. If we need to
+pickle instances of ``Point`` or its owning class ``Vertex``, we at least need
+to define a ``__getstate__`` that doesn't include the ``_parents`` dictionary.
+Below we define both a ``__getstate__`` and a ``__setstate__`` that package up
+the minimal form of our ``Point`` class::
+
+    class Point(MutableComposite):
+        # ...
+
+        def __getstate__(self):
+            return self.x, self.y
+
+        def __setstate__(self, state):
+            self.x, self.y = state
+
+As with :class:`.Mutable`, the :class:`.MutableComposite` augments the
+pickling process of the parent's object-relational state so that the
+:meth:`MutableBase._parents` collection is restored to all ``Point`` objects.
+
+"""
+from collections import defaultdict
+import weakref
+
+from .. import event
+from .. import inspect
+from .. import types
+from ..orm import Mapper
+from ..orm import mapper
+from ..orm.attributes import flag_modified
+from ..sql.base import SchemaEventTarget
+from ..util import memoized_property
+
+
+class MutableBase(object):
+    """Common base class to :class:`.Mutable`
+    and :class:`.MutableComposite`.
+
+    """
+
+    @memoized_property
+    def _parents(self):
+        """Dictionary of parent object's :class:`.InstanceState`->attribute
+        name on the parent.
+
+        This attribute is a so-called "memoized" property.  It initializes
+        itself with a new ``weakref.WeakKeyDictionary`` the first time
+        it is accessed, returning the same object upon subsequent access.
+
+        .. versionchanged:: 1.4 the :class:`.InstanceState` is now used
+           as the key in the weak dictionary rather than the instance
+           itself.
+
+        """
+
+        return weakref.WeakKeyDictionary()
+
+    @classmethod
+    def coerce(cls, key, value):
+        """Given a value, coerce it into the target type.
+
+        Can be overridden by custom subclasses to coerce incoming
+        data into a particular type.
+
+        By default, raises ``ValueError``.
+
+        This method is called in different scenarios depending on if
+        the parent class is of type :class:`.Mutable` or of type
+        :class:`.MutableComposite`.  In the case of the former, it is called
+        for both attribute-set operations as well as during ORM loading
+        operations.  For the latter, it is only called during attribute-set
+        operations; the mechanics of the :func:`.composite` construct
+        handle coercion during load operations.
+
+
+        :param key: string name of the ORM-mapped attribute being set.
+        :param value: the incoming value.
+        :return: the method should return the coerced value, or raise
+         ``ValueError`` if the coercion cannot be completed.
+
+        """
+        if value is None:
+            return None
+        msg = "Attribute '%s' does not accept objects of type %s"
+        raise ValueError(msg % (key, type(value)))
+
+    @classmethod
+    def _get_listen_keys(cls, attribute):
+        """Given a descriptor attribute, return a ``set()`` of the attribute
+        keys which indicate a change in the state of this attribute.
+
+        This is normally just ``set([attribute.key])``, but can be overridden
+        to provide for additional keys.  E.g. a :class:`.MutableComposite`
+        augments this set with the attribute keys associated with the columns
+        that comprise the composite value.
+
+        This collection is consulted in the case of intercepting the
+        :meth:`.InstanceEvents.refresh` and
+        :meth:`.InstanceEvents.refresh_flush` events, which pass along a list
+        of attribute names that have been refreshed; the list is compared
+        against this set to determine if action needs to be taken.
+
+        .. versionadded:: 1.0.5
+
+        """
+        return {attribute.key}
+
+    @classmethod
+    def _listen_on_attribute(cls, attribute, coerce, parent_cls):
+        """Establish this type as a mutation listener for the given
+        mapped descriptor.
+
+        """
+        key = attribute.key
+        if parent_cls is not attribute.class_:
+            return
+
+        # rely on "propagate" here
+        parent_cls = attribute.class_
+
+        listen_keys = cls._get_listen_keys(attribute)
+
+        def load(state, *args):
+            """Listen for objects loaded or refreshed.
+
+            Wrap the target data member's value with
+            ``Mutable``.
+
+            """
+            val = state.dict.get(key, None)
+            if val is not None:
+                if coerce:
+                    val = cls.coerce(key, val)
+                    state.dict[key] = val
+                val._parents[state] = key
+
+        def load_attrs(state, ctx, attrs):
+            if not attrs or listen_keys.intersection(attrs):
+                load(state)
+
+        def set_(target, value, oldvalue, initiator):
+            """Listen for set/replace events on the target
+            data member.
+
+            Establish a weak reference to the parent object
+            on the incoming value, remove it for the one
+            outgoing.
+
+            """
+            if value is oldvalue:
+                return value
+
+            if not isinstance(value, cls):
+                value = cls.coerce(key, value)
+            if value is not None:
+                value._parents[target] = key
+            if isinstance(oldvalue, cls):
+                oldvalue._parents.pop(inspect(target), None)
+            return value
+
+        def pickle(state, state_dict):
+            val = state.dict.get(key, None)
+            if val is not None:
+                if "ext.mutable.values" not in state_dict:
+                    state_dict["ext.mutable.values"] = defaultdict(list)
+                state_dict["ext.mutable.values"][key].append(val)
+
+        def unpickle(state, state_dict):
+            if "ext.mutable.values" in state_dict:
+                collection = state_dict["ext.mutable.values"]
+                if isinstance(collection, list):
+                    # legacy format
+                    for val in collection:
+                        val._parents[state] = key
+                else:
+                    for val in state_dict["ext.mutable.values"][key]:
+                        val._parents[state] = key
+
+        event.listen(parent_cls, "load", load, raw=True, propagate=True)
+        event.listen(
+            parent_cls, "refresh", load_attrs, raw=True, propagate=True
+        )
+        event.listen(
+            parent_cls, "refresh_flush", load_attrs, raw=True, propagate=True
+        )
+        event.listen(
+            attribute, "set", set_, raw=True, retval=True, propagate=True
+        )
+        event.listen(parent_cls, "pickle", pickle, raw=True, propagate=True)
+        event.listen(
+            parent_cls, "unpickle", unpickle, raw=True, propagate=True
+        )
+
+
+class Mutable(MutableBase):
+    """Mixin that defines transparent propagation of change
+    events to a parent object.
+
+    See the example in :ref:`mutable_scalars` for usage information.
+
+    """
+
+    def changed(self):
+        """Subclasses should call this method whenever change events occur."""
+
+        for parent, key in self._parents.items():
+            flag_modified(parent.obj(), key)
+
+    @classmethod
+    def associate_with_attribute(cls, attribute):
+        """Establish this type as a mutation listener for the given
+        mapped descriptor.
+
+        """
+        cls._listen_on_attribute(attribute, True, attribute.class_)
+
+    @classmethod
+    def associate_with(cls, sqltype):
+        """Associate this wrapper with all future mapped columns
+        of the given type.
+
+        This is a convenience method that calls
+        ``associate_with_attribute`` automatically.
+
+        .. warning::
+
+           The listeners established by this method are *global*
+           to all mappers, and are *not* garbage collected.   Only use
+           :meth:`.associate_with` for types that are permanent to an
+           application, not with ad-hoc types else this will cause unbounded
+           growth in memory usage.
+
+        """
+
+        def listen_for_type(mapper, class_):
+            if mapper.non_primary:
+                return
+            for prop in mapper.column_attrs:
+                if isinstance(prop.columns[0].type, sqltype):
+                    cls.associate_with_attribute(getattr(class_, prop.key))
+
+        event.listen(mapper, "mapper_configured", listen_for_type)
+
+    @classmethod
+    def as_mutable(cls, sqltype):
+        """Associate a SQL type with this mutable Python type.
+
+        This establishes listeners that will detect ORM mappings against
+        the given type, adding mutation event trackers to those mappings.
+
+        The type is returned, unconditionally as an instance, so that
+        :meth:`.as_mutable` can be used inline::
+
+            Table('mytable', metadata,
+                Column('id', Integer, primary_key=True),
+                Column('data', MyMutableType.as_mutable(PickleType))
+            )
+
+        Note that the returned type is always an instance, even if a class
+        is given, and that only columns which are declared specifically with
+        that type instance receive additional instrumentation.
+
+        To associate a particular mutable type with all occurrences of a
+        particular type, use the :meth:`.Mutable.associate_with` classmethod
+        of the particular :class:`.Mutable` subclass to establish a global
+        association.
+
+        .. warning::
+
+           The listeners established by this method are *global*
+           to all mappers, and are *not* garbage collected.   Only use
+           :meth:`.as_mutable` for types that are permanent to an application,
+           not with ad-hoc types else this will cause unbounded growth
+           in memory usage.
+
+        """
+        sqltype = types.to_instance(sqltype)
+
+        # a SchemaType will be copied when the Column is copied,
+        # and we'll lose our ability to link that type back to the original.
+        # so track our original type w/ columns
+        if isinstance(sqltype, SchemaEventTarget):
+
+            @event.listens_for(sqltype, "before_parent_attach")
+            def _add_column_memo(sqltyp, parent):
+                parent.info["_ext_mutable_orig_type"] = sqltyp
+
+            schema_event_check = True
+        else:
+            schema_event_check = False
+
+        def listen_for_type(mapper, class_):
+            if mapper.non_primary:
+                return
+            for prop in mapper.column_attrs:
+                if (
+                    schema_event_check
+                    and hasattr(prop.expression, "info")
+                    and prop.expression.info.get("_ext_mutable_orig_type")
+                    is sqltype
+                ) or (prop.columns[0].type is sqltype):
+                    cls.associate_with_attribute(getattr(class_, prop.key))
+
+        event.listen(mapper, "mapper_configured", listen_for_type)
+
+        return sqltype
+
+
+class MutableComposite(MutableBase):
+    """Mixin that defines transparent propagation of change
+    events on a SQLAlchemy "composite" object to its
+    owning parent or parents.
+
+    See the example in :ref:`mutable_composites` for usage information.
+
+    """
+
+    @classmethod
+    def _get_listen_keys(cls, attribute):
+        return {attribute.key}.union(attribute.property._attribute_keys)
+
+    def changed(self):
+        """Subclasses should call this method whenever change events occur."""
+
+        for parent, key in self._parents.items():
+
+            prop = parent.mapper.get_property(key)
+            for value, attr_name in zip(
+                self.__composite_values__(), prop._attribute_keys
+            ):
+                setattr(parent.obj(), attr_name, value)
+
+
+def _setup_composite_listener():
+    def _listen_for_type(mapper, class_):
+        for prop in mapper.iterate_properties:
+            if (
+                hasattr(prop, "composite_class")
+                and isinstance(prop.composite_class, type)
+                and issubclass(prop.composite_class, MutableComposite)
+            ):
+                prop.composite_class._listen_on_attribute(
+                    getattr(class_, prop.key), False, class_
+                )
+
+    if not event.contains(Mapper, "mapper_configured", _listen_for_type):
+        event.listen(Mapper, "mapper_configured", _listen_for_type)
+
+
+_setup_composite_listener()
+
+
+class MutableDict(Mutable, dict):
+    """A dictionary type that implements :class:`.Mutable`.
+
+    The :class:`.MutableDict` object implements a dictionary that will
+    emit change events to the underlying mapping when the contents of
+    the dictionary are altered, including when values are added or removed.
+
+    Note that :class:`.MutableDict` does **not** apply mutable tracking to  the
+    *values themselves* inside the dictionary. Therefore it is not a sufficient
+    solution for the use case of tracking deep changes to a *recursive*
+    dictionary structure, such as a JSON structure.  To support this use case,
+    build a subclass of  :class:`.MutableDict` that provides appropriate
+    coercion to the values placed in the dictionary so that they too are
+    "mutable", and emit events up to their parent structure.
+
+    .. seealso::
+
+        :class:`.MutableList`
+
+        :class:`.MutableSet`
+
+    """
+
+    def __setitem__(self, key, value):
+        """Detect dictionary set events and emit change events."""
+        dict.__setitem__(self, key, value)
+        self.changed()
+
+    def setdefault(self, key, value):
+        result = dict.setdefault(self, key, value)
+        self.changed()
+        return result
+
+    def __delitem__(self, key):
+        """Detect dictionary del events and emit change events."""
+        dict.__delitem__(self, key)
+        self.changed()
+
+    def update(self, *a, **kw):
+        dict.update(self, *a, **kw)
+        self.changed()
+
+    def pop(self, *arg):
+        result = dict.pop(self, *arg)
+        self.changed()
+        return result
+
+    def popitem(self):
+        result = dict.popitem(self)
+        self.changed()
+        return result
+
+    def clear(self):
+        dict.clear(self)
+        self.changed()
+
+    @classmethod
+    def coerce(cls, key, value):
+        """Convert plain dictionary to instance of this class."""
+        if not isinstance(value, cls):
+            if isinstance(value, dict):
+                return cls(value)
+            return Mutable.coerce(key, value)
+        else:
+            return value
+
+    def __getstate__(self):
+        return dict(self)
+
+    def __setstate__(self, state):
+        self.update(state)
+
+
+class MutableList(Mutable, list):
+    """A list type that implements :class:`.Mutable`.
+
+    The :class:`.MutableList` object implements a list that will
+    emit change events to the underlying mapping when the contents of
+    the list are altered, including when values are added or removed.
+
+    Note that :class:`.MutableList` does **not** apply mutable tracking to  the
+    *values themselves* inside the list. Therefore it is not a sufficient
+    solution for the use case of tracking deep changes to a *recursive*
+    mutable structure, such as a JSON structure.  To support this use case,
+    build a subclass of  :class:`.MutableList` that provides appropriate
+    coercion to the values placed in the dictionary so that they too are
+    "mutable", and emit events up to their parent structure.
+
+    .. versionadded:: 1.1
+
+    .. seealso::
+
+        :class:`.MutableDict`
+
+        :class:`.MutableSet`
+
+    """
+
+    def __reduce_ex__(self, proto):
+        return (self.__class__, (list(self),))
+
+    # needed for backwards compatibility with
+    # older pickles
+    def __setstate__(self, state):
+        self[:] = state
+
+    def __setitem__(self, index, value):
+        """Detect list set events and emit change events."""
+        list.__setitem__(self, index, value)
+        self.changed()
+
+    def __setslice__(self, start, end, value):
+        """Detect list set events and emit change events."""
+        list.__setslice__(self, start, end, value)
+        self.changed()
+
+    def __delitem__(self, index):
+        """Detect list del events and emit change events."""
+        list.__delitem__(self, index)
+        self.changed()
+
+    def __delslice__(self, start, end):
+        """Detect list del events and emit change events."""
+        list.__delslice__(self, start, end)
+        self.changed()
+
+    def pop(self, *arg):
+        result = list.pop(self, *arg)
+        self.changed()
+        return result
+
+    def append(self, x):
+        list.append(self, x)
+        self.changed()
+
+    def extend(self, x):
+        list.extend(self, x)
+        self.changed()
+
+    def __iadd__(self, x):
+        self.extend(x)
+        return self
+
+    def insert(self, i, x):
+        list.insert(self, i, x)
+        self.changed()
+
+    def remove(self, i):
+        list.remove(self, i)
+        self.changed()
+
+    def clear(self):
+        list.clear(self)
+        self.changed()
+
+    def sort(self, **kw):
+        list.sort(self, **kw)
+        self.changed()
+
+    def reverse(self):
+        list.reverse(self)
+        self.changed()
+
+    @classmethod
+    def coerce(cls, index, value):
+        """Convert plain list to instance of this class."""
+        if not isinstance(value, cls):
+            if isinstance(value, list):
+                return cls(value)
+            return Mutable.coerce(index, value)
+        else:
+            return value
+
+
+class MutableSet(Mutable, set):
+    """A set type that implements :class:`.Mutable`.
+
+    The :class:`.MutableSet` object implements a set that will
+    emit change events to the underlying mapping when the contents of
+    the set are altered, including when values are added or removed.
+
+    Note that :class:`.MutableSet` does **not** apply mutable tracking to  the
+    *values themselves* inside the set. Therefore it is not a sufficient
+    solution for the use case of tracking deep changes to a *recursive*
+    mutable structure.  To support this use case,
+    build a subclass of  :class:`.MutableSet` that provides appropriate
+    coercion to the values placed in the dictionary so that they too are
+    "mutable", and emit events up to their parent structure.
+
+    .. versionadded:: 1.1
+
+    .. seealso::
+
+        :class:`.MutableDict`
+
+        :class:`.MutableList`
+
+
+    """
+
+    def update(self, *arg):
+        set.update(self, *arg)
+        self.changed()
+
+    def intersection_update(self, *arg):
+        set.intersection_update(self, *arg)
+        self.changed()
+
+    def difference_update(self, *arg):
+        set.difference_update(self, *arg)
+        self.changed()
+
+    def symmetric_difference_update(self, *arg):
+        set.symmetric_difference_update(self, *arg)
+        self.changed()
+
+    def __ior__(self, other):
+        self.update(other)
+        return self
+
+    def __iand__(self, other):
+        self.intersection_update(other)
+        return self
+
+    def __ixor__(self, other):
+        self.symmetric_difference_update(other)
+        return self
+
+    def __isub__(self, other):
+        self.difference_update(other)
+        return self
+
+    def add(self, elem):
+        set.add(self, elem)
+        self.changed()
+
+    def remove(self, elem):
+        set.remove(self, elem)
+        self.changed()
+
+    def discard(self, elem):
+        set.discard(self, elem)
+        self.changed()
+
+    def pop(self, *arg):
+        result = set.pop(self, *arg)
+        self.changed()
+        return result
+
+    def clear(self):
+        set.clear(self)
+        self.changed()
+
+    @classmethod
+    def coerce(cls, index, value):
+        """Convert plain set to instance of this class."""
+        if not isinstance(value, cls):
+            if isinstance(value, set):
+                return cls(value)
+            return Mutable.coerce(index, value)
+        else:
+            return value
+
+    def __getstate__(self):
+        return set(self)
+
+    def __setstate__(self, state):
+        self.update(state)
+
+    def __reduce_ex__(self, proto):
+        return (self.__class__, (list(self),))