django1/docs/ref/exceptions.txt

=================
Django Exceptions
=================

Django raises some of its own exceptions as well as standard Python exceptions.

Django Core Exceptions
======================

.. module:: django.core.exceptions
    :synopsis: Django core exceptions

Django core exception classes are defined in ``django.core.exceptions``.

``AppRegistryNotReady``
-----------------------

.. exception:: AppRegistryNotReady

    This exception is raised when attempting to use models before the :ref:`app
    loading process <app-loading-process>`, which initializes the ORM, is
    complete.

``ObjectDoesNotExist``
----------------------

.. exception:: ObjectDoesNotExist

    The base class for :exc:`~django.db.models.Model.DoesNotExist` exceptions;
    a ``try/except`` for ``ObjectDoesNotExist`` will catch
    :exc:`~django.db.models.Model.DoesNotExist` exceptions for all models.

    See :meth:`~django.db.models.query.QuerySet.get()` for further information
    on :exc:`ObjectDoesNotExist` and :exc:`~django.db.models.Model.DoesNotExist`.

``EmptyResultSet``
------------------

.. exception:: EmptyResultSet

    ``EmptyResultSet`` may be raised during query generation if a query won't
    return any results. Most Django projects won't encounter this exception,
    but it might be useful for implementing custom lookups and expressions.

    .. versionchanged:: 1.11

        In older versions, it's only importable from ``django.db.models.sql``.

``FieldDoesNotExist``
---------------------

.. exception:: FieldDoesNotExist

    The ``FieldDoesNotExist`` exception is raised by a model's
    ``_meta.get_field()`` method when the requested field does not exist on the
    model or on the model's parents.

``MultipleObjectsReturned``
---------------------------

.. exception:: MultipleObjectsReturned

    The :exc:`MultipleObjectsReturned` exception is raised by a query if only
    one object is expected, but multiple objects are returned. A base version
    of this exception is provided in :mod:`django.core.exceptions`; each model
    class contains a subclassed version that can be used to identify the
    specific object type that has returned multiple objects.

    See :meth:`~django.db.models.query.QuerySet.get()` for further information.

``SuspiciousOperation``
-----------------------

.. exception:: SuspiciousOperation

    The :exc:`SuspiciousOperation` exception is raised when a user has
    performed an operation that should be considered suspicious from a security
    perspective, such as tampering with a session cookie. Subclasses of
    ``SuspiciousOperation`` include:

    * ``DisallowedHost``
    * ``DisallowedModelAdminLookup``
    * ``DisallowedModelAdminToField``
    * ``DisallowedRedirect``
    * ``InvalidSessionKey``
    * ``RequestDataTooBig``
    * ``SuspiciousFileOperation``
    * ``SuspiciousMultipartForm``
    * ``SuspiciousSession``
    * ``TooManyFieldsSent``

    If a ``SuspiciousOperation`` exception reaches the WSGI handler level it is
    logged at the ``Error`` level and results in
    a :class:`~django.http.HttpResponseBadRequest`. See the :doc:`logging
    documentation </topics/logging/>` for more information.

``PermissionDenied``
--------------------

.. exception:: PermissionDenied

    The :exc:`PermissionDenied` exception is raised when a user does not have
    permission to perform the action requested.

``ViewDoesNotExist``
--------------------

.. exception:: ViewDoesNotExist

    The :exc:`ViewDoesNotExist` exception is raised by
    :mod:`django.urls` when a requested view does not exist.

``MiddlewareNotUsed``
---------------------

.. exception:: MiddlewareNotUsed

    The :exc:`MiddlewareNotUsed` exception is raised when a middleware is not
    used in the server configuration.

``ImproperlyConfigured``
------------------------

.. exception:: ImproperlyConfigured

    The :exc:`ImproperlyConfigured` exception is raised when Django is
    somehow improperly configured -- for example, if a value in ``settings.py``
    is incorrect or unparseable.

``FieldError``
--------------

.. exception:: FieldError

    The :exc:`FieldError` exception is raised when there is a problem with a
    model field. This can happen for several reasons:

    - A field in a model clashes with a field of the same name from an
      abstract base class
    - An infinite loop is caused by ordering
    - A keyword cannot be parsed from the filter parameters
    - A field cannot be determined from a keyword in the query
      parameters
    - A join is not permitted on the specified field
    - A field name is invalid
    - A query contains invalid order_by arguments

``ValidationError``
-------------------

.. exception:: ValidationError

    The :exc:`ValidationError` exception is raised when data fails form or
    model field validation. For more information about validation, see
    :doc:`Form and Field Validation </ref/forms/validation>`,
    :ref:`Model Field Validation <validating-objects>` and the
    :doc:`Validator Reference </ref/validators>`.

``NON_FIELD_ERRORS``
~~~~~~~~~~~~~~~~~~~~

.. data:: NON_FIELD_ERRORS

``ValidationError``\s that don't belong to a particular field in a form
or model are classified as ``NON_FIELD_ERRORS``. This constant is used
as a key in dictionaries that otherwise map fields to their respective
list of errors.

.. currentmodule:: django.urls

URL Resolver exceptions
=======================

URL Resolver exceptions are defined in ``django.urls``.

``Resolver404``
---------------

.. exception:: Resolver404

    The :exc:`Resolver404` exception is raised by
    :func:`~django.urls.resolve()` if the path passed to ``resolve()`` doesn't
    map to a view. It's a subclass of :class:`django.http.Http404`.

``NoReverseMatch``
------------------

.. exception:: NoReverseMatch

    The :exc:`NoReverseMatch` exception is raised by :mod:`django.urls` when a
    matching URL in your URLconf cannot be identified based on the parameters
    supplied.

.. currentmodule:: django.db

Database Exceptions
===================

Database exceptions may be imported from ``django.db``.

Django wraps the standard database exceptions so that your Django code has a
guaranteed common implementation of these classes.

.. exception:: Error
.. exception:: InterfaceError
.. exception:: DatabaseError
.. exception:: DataError
.. exception:: OperationalError
.. exception:: IntegrityError
.. exception:: InternalError
.. exception:: ProgrammingError
.. exception:: NotSupportedError

The Django wrappers for database exceptions behave exactly the same as
the underlying database exceptions. See :pep:`249`, the Python Database API
Specification v2.0, for further information.

As per :pep:`3134`, a ``__cause__`` attribute is set with the original
(underlying) database exception, allowing access to any additional
information provided. (Note that this attribute is available under
both Python 2 and Python 3, although :pep:`3134` normally only applies
to Python 3. To avoid unexpected differences with Python 3, Django will also
ensure that the exception made available via ``__cause__`` has a usable
``__traceback__`` attribute.)

.. exception:: models.ProtectedError

Raised to prevent deletion of referenced objects when using
:attr:`django.db.models.PROTECT`. :exc:`models.ProtectedError` is a subclass
of :exc:`IntegrityError`.

.. currentmodule:: django.http

Http Exceptions
===============

Http exceptions may be imported from ``django.http``.

``UnreadablePostError``
-----------------------

.. exception:: UnreadablePostError

    :exc:`UnreadablePostError` is raised when a user cancels an upload.

Transaction Exceptions
======================

.. currentmodule:: django.db.transaction

Transaction exceptions are defined in ``django.db.transaction``.

``TransactionManagementError``
------------------------------

.. exception:: TransactionManagementError

    :exc:`TransactionManagementError` is raised for any and all problems
    related to database transactions.

.. currentmodule:: django.test

Testing Framework Exceptions
============================

Exceptions provided by the ``django.test`` package.

``RedirectCycleError``
----------------------

.. exception:: client.RedirectCycleError

    :exc:`~client.RedirectCycleError` is raised when the test client detects a
    loop or an overly long chain of redirects.

Python Exceptions
=================

Django raises built-in Python exceptions when appropriate as well. See the
Python documentation for further information on the :ref:`bltin-exceptions`.