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diff --git a/lib/sqlalchemy/inspection.py b/lib/sqlalchemy/inspection.py
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+# sqlalchemy/inspect.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
+
+"""The inspection module provides the :func:`_sa.inspect` function,
+which delivers runtime information about a wide variety
+of SQLAlchemy objects, both within the Core as well as the
+ORM.
+
+The :func:`_sa.inspect` function is the entry point to SQLAlchemy's
+public API for viewing the configuration and construction
+of in-memory objects.   Depending on the type of object
+passed to :func:`_sa.inspect`, the return value will either be
+a related object which provides a known interface, or in many
+cases it will return the object itself.
+
+The rationale for :func:`_sa.inspect` is twofold.  One is that
+it replaces the need to be aware of a large variety of "information
+getting" functions in SQLAlchemy, such as
+:meth:`_reflection.Inspector.from_engine` (deprecated in 1.4),
+:func:`.orm.attributes.instance_state`, :func:`_orm.class_mapper`,
+and others.    The other is that the return value of :func:`_sa.inspect`
+is guaranteed to obey a documented API, thus allowing third party
+tools which build on top of SQLAlchemy configurations to be constructed
+in a forwards-compatible way.
+
+"""
+
+from . import exc
+from . import util
+
+
+_registrars = util.defaultdict(list)
+
+
+def inspect(subject, raiseerr=True):
+    """Produce an inspection object for the given target.
+
+    The returned value in some cases may be the
+    same object as the one given, such as if a
+    :class:`_orm.Mapper` object is passed.   In other
+    cases, it will be an instance of the registered
+    inspection type for the given object, such as
+    if an :class:`_engine.Engine` is passed, an
+    :class:`_reflection.Inspector` object is returned.
+
+    :param subject: the subject to be inspected.
+    :param raiseerr: When ``True``, if the given subject
+     does not
+     correspond to a known SQLAlchemy inspected type,
+     :class:`sqlalchemy.exc.NoInspectionAvailable`
+     is raised.  If ``False``, ``None`` is returned.
+
+    """
+    type_ = type(subject)
+    for cls in type_.__mro__:
+        if cls in _registrars:
+            reg = _registrars[cls]
+            if reg is True:
+                return subject
+            ret = reg(subject)
+            if ret is not None:
+                break
+    else:
+        reg = ret = None
+
+    if raiseerr and (reg is None or ret is None):
+        raise exc.NoInspectionAvailable(
+            "No inspection system is "
+            "available for object of type %s" % type_
+        )
+    return ret
+
+
+def _inspects(*types):
+    def decorate(fn_or_cls):
+        for type_ in types:
+            if type_ in _registrars:
+                raise AssertionError(
+                    "Type %s is already " "registered" % type_
+                )
+            _registrars[type_] = fn_or_cls
+        return fn_or_cls
+
+    return decorate
+
+
+def _self_inspects(cls):
+    _inspects(cls)(True)
+    return cls