Django Exceptions. Django Software

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Django Documentation, Release 1.11.8.dev20171115160334

Examples: from django.core

import management from django.core.management.commands

import loaddata management.call_command( 'flush' , verbosity= 0 , interactive=False) management.call_command( 'loaddata' , 'test_data' , verbosity= 0 ) management.call_command(loaddata.Command(), 'test_data' , verbosity= 0 )

Note that command options that take no arguments are passed as keywords with True or False, as you can see with the interactive option above.

Named arguments can be passed by using either one of the following syntaxes:

# Similar to the command line management.call_command( 'dumpdata' , '--natural-foreign' )

# Named argument similar to the command line minus the initial dashes and

# with internal dashes replaced by underscores management.call_command( 'dumpdata' , natural_foreign=True)

# `use_natural_foreign_keys` is the option destination variable management.call_command( 'dumpdata' , use_natural_foreign_keys=True)

Some command options have different names when using call_command() instead of django-admin or manage.py

For example, django-admin createsuperuser --no-input translates to call_command('createsuperuser', interactive=False) .

To find what keyword argument name to use for call_command(), check the command’s source code for the dest argument passed to parser.add_argument() .

Command options which take multiple options are passed a list: management.call_command( 'dumpdata' , exclude=[ 'contenttypes' , 'auth' ])

The return value of the call_command() function is the same as the return value of the handle() method of the command.

call_command() now returns the value received from the command.handle() method. It now also accepts a command object as the first argument.

6.9.1 Output redirection

Note that you can redirect standard output and error streams as all commands support the stdout and stderr options. For example, you could write: with open ( '/path/to/command_output' ) as f: management.call_command( 'dumpdata' , stdout=f)

6.10 Django Exceptions

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

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6.10.1 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

app loading process , which initializes the

ORM, is complete.

ObjectDoesNotExist exception ObjectDoesNotExist

The base class for

DoesNotExist

exceptions; a try/except for ObjectDoesNotExist will catch

DoesNotExist

exceptions for all models.

See

get()

for further information on

ObjectDoesNotExist

and

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.

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

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

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

get()

for further information.

SuspiciousOperation exception SuspiciousOperation

The

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

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• 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

HttpResponseBadRequest . See the

logging documentation

for more information.

PermissionDenied exception PermissionDenied

The

PermissionDenied

exception is raised when a user does not have permission to perform the action requested.

ViewDoesNotExist exception ViewDoesNotExist

The

ViewDoesNotExist

exception is raised by

django.urls

when a requested view does not exist.

MiddlewareNotUsed exception MiddlewareNotUsed

The

MiddlewareNotUsed

exception is raised when a middleware is not used in the server configuration.

ImproperlyConfigured exception ImproperlyConfigured

The

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

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

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• 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

ValidationError

exception is raised when data fails form or model field validation. For more information about validation, see

Form and Field Validation ,

Model Field Validation

and the

Validator Reference .

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.

6.10.2 URL Resolver exceptions

URL Resolver exceptions are defined in django.urls.

Deprecated since version 1.10: In older versions, these exceptions are located in django.core.urlresolvers.

Importing from the old location will continue to work until Django 2.0.

Resolver404 exception Resolver404

The

Resolver404

exception is raised by

resolve()

if the path passed to resolve() doesn’t map to a view. It’s a subclass of

django.http.Http404

NoReverseMatch exception NoReverseMatch

The

NoReverseMatch

exception is raised by

django.urls

when a matching URL in your URLconf cannot be identified based on the parameters supplied.

6.10.3 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

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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.)

The __traceback__ attribute described above was added.

exception models.ProtectedError

Raised to prevent deletion of referenced objects when using

django.db.models.PROTECT

models.

ProtectedError

is a subclass of

IntegrityError .