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django/docs/ref/exceptions.txt
wrwrwr 056a3c6c37 Fixed #23682 -- Enhanced circular redirects detection in tests.
When the test client detects a redirect to a URL seen in the
currently followed chain it will now raise a RedirectCycleError
instead of just returning the first repeated response.

It will also complain when a single chain of redirects is longer
than 20, as this often means a redirect loop with varying URLs,
and even if it's not actually one, such long chains are likely
to be treated as loops by browsers.

Thanks Preston Timmons, Berker Peksag, and Tim Graham for reviews.
2014-11-25 10:12:28 -05:00

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=================
Django Exceptions
=================
Django raises some Django specific exceptions as well as many standard
Python exceptions.
Django Core Exceptions
======================
.. module:: django.core.exceptions
:synopsis: Django core exceptions
Django core exception classes are defined in :mod:`django.core.exceptions`.
ObjectDoesNotExist and DoesNotExist
-----------------------------------
.. exception:: DoesNotExist
The ``DoesNotExist`` exception is raised when an object is not found for
the given parameters of a query. Django provides a ``DoesNotExist``
exception as an attribute of each model class to identify the class of
object that could not be found and to allow you to catch a particular model
class with ``try/except``.
.. exception:: ObjectDoesNotExist
The base class for ``DoesNotExist`` exceptions; a ``try/except`` for
``ObjectDoesNotExist`` will catch ``DoesNotExist`` exceptions for all
models.
See :meth:`~django.db.models.query.QuerySet.get()` for further information
on :exc:`ObjectDoesNotExist` and :exc:`DoesNotExist`.
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
* SuspiciousFileOperation
* SuspiciousMultipartForm
* SuspiciousSession
* WizardViewCookieModified
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.core.urlresolvers` 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.core.urlresolvers
URL Resolver exceptions
=======================
URL Resolver exceptions are defined in :mod:`django.core.urlresolvers`.
Resolver404
--------------
.. exception:: Resolver404
The :exc:`Resolver404` exception is raised by
:func:`django.core.urlresolvers.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.core.urlresolvers` when a matching URL in your URLconf
cannot be identified based on the parameters supplied.
.. currentmodule:: django.db
Database Exceptions
===================
Database exceptions are provided in :mod:`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.)
.. 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 are provided in :mod:`django.http`.
.. exception:: UnreadablePostError
The :exc:`UnreadablePostError` is raised when a user cancels an upload.
.. currentmodule:: django.db.transaction
Transaction Exceptions
======================
Transaction exceptions are defined in :mod:`django.db.transaction`.
.. exception:: TransactionManagementError
The :exc:`TransactionManagementError` is raised for any and all problems
related to database transactions.
.. currentmodule:: django.test
Testing Framework Exceptions
============================
Exceptions provided by the :mod:`django.test` package.
.. exception:: client.RedirectCycleError
.. versionadded:: 1.8
: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`.