django1/docs/ref/exceptions.txt

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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`.
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.
.. versionchanged:: 1.8
This exception was previously defined only in
``django.db.models.fields`` and wasn't part of the public API.
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`.