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# sqlalchemy/inspect.py
# Copyright (C) 2005-2017 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
"""The inspection module provides the :func:`.inspect` function,
which delivers runtime information about a wide variety
of SQLAlchemy objects, both within the Core as well as the
ORM.
The :func:`.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:`.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:`.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:`.Inspector.from_engine`,
:func:`.orm.attributes.instance_state`, :func:`.orm.class_mapper`,
and others. The other is that the return value of :func:`.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.
.. versionadded:: 0.8 The :func:`.inspect` system is introduced
as of version 0.8.
"""
from . import util, exc
_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:`.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:`.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
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