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The last component of the dotted path to the application module is consistently referenced as the application "label". For instance it's AppConfig.label. appname could be confused with AppConfig.name, which is the full dotted path.
391 lines
14 KiB
Plaintext
391 lines
14 KiB
Plaintext
====================================
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Writing custom django-admin commands
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====================================
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.. module:: django.core.management
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Applications can register their own actions with ``manage.py``. For example,
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you might want to add a ``manage.py`` action for a Django app that you're
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distributing. In this document, we will be building a custom ``closepoll``
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command for the ``polls`` application from the
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:doc:`tutorial</intro/tutorial01>`.
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To do this, just add a ``management/commands`` directory to the application.
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Django will register a ``manage.py`` command for each Python module in that
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directory whose name doesn't begin with an underscore. For example::
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polls/
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__init__.py
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models.py
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management/
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__init__.py
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commands/
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__init__.py
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_private.py
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closepoll.py
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tests.py
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views.py
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In this example, the ``closepoll`` command will be made available to any project
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that includes the ``polls`` application in :setting:`INSTALLED_APPS`.
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The ``_private.py`` module will not be available as a management command.
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The ``closepoll.py`` module has only one requirement -- it must define a class
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``Command`` that extends :class:`BaseCommand` or one of its
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:ref:`subclasses<ref-basecommand-subclasses>`.
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.. admonition:: Standalone scripts
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Custom management commands are especially useful for running standalone
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scripts or for scripts that are periodically executed from the UNIX crontab
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or from Windows scheduled tasks control panel.
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To implement the command, edit ``polls/management/commands/closepoll.py`` to
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look like this:
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.. code-block:: python
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from django.core.management.base import BaseCommand, CommandError
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from polls.models import Poll
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class Command(BaseCommand):
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args = '<poll_id poll_id ...>'
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help = 'Closes the specified poll for voting'
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def handle(self, *args, **options):
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for poll_id in args:
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try:
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poll = Poll.objects.get(pk=int(poll_id))
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except Poll.DoesNotExist:
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raise CommandError('Poll "%s" does not exist' % poll_id)
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poll.opened = False
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poll.save()
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self.stdout.write('Successfully closed poll "%s"' % poll_id)
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.. _management-commands-output:
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.. note::
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When you are using management commands and wish to provide console
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output, you should write to ``self.stdout`` and ``self.stderr``,
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instead of printing to ``stdout`` and ``stderr`` directly. By
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using these proxies, it becomes much easier to test your custom
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command. Note also that you don't need to end messages with a newline
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character, it will be added automatically, unless you specify the ``ending``
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parameter::
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self.stdout.write("Unterminated line", ending='')
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The new custom command can be called using ``python manage.py closepoll
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<poll_id>``.
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The ``handle()`` method takes zero or more ``poll_ids`` and sets ``poll.opened``
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to ``False`` for each one. If the user referenced any nonexistent polls, a
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:class:`CommandError` is raised. The ``poll.opened`` attribute does not exist
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in the :doc:`tutorial</intro/tutorial01>` and was added to
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``polls.models.Poll`` for this example.
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The same ``closepoll`` could be easily modified to delete a given poll instead
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of closing it by accepting additional command line options. These custom options
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must be added to :attr:`~BaseCommand.option_list` like this:
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.. code-block:: python
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from optparse import make_option
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class Command(BaseCommand):
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option_list = BaseCommand.option_list + (
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make_option('--delete',
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action='store_true',
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dest='delete',
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default=False,
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help='Delete poll instead of closing it'),
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)
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def handle(self, *args, **options):
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# ...
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if options['delete']:
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poll.delete()
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# ...
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The option (``delete`` in our example) is available in the options dict
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parameter of the handle method. See the :py:mod:`optparse` Python documentation
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for more about ``make_option`` usage.
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In addition to being able to add custom command line options, all
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:doc:`management commands</ref/django-admin>` can accept some
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default options such as :djadminopt:`--verbosity` and :djadminopt:`--traceback`.
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.. _management-commands-and-locales:
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Management commands and locales
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===============================
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By default, the :meth:`BaseCommand.execute` method sets the hardcoded 'en-us'
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locale because some commands shipped with Django perform several tasks
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(for example, user-facing content rendering and database population) that
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require a system-neutral string language (for which we use 'en-us').
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If, for some reason, your custom management command needs to use a fixed locale
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different from 'en-us', you should manually activate and deactivate it in your
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:meth:`~BaseCommand.handle` or :meth:`~NoArgsCommand.handle_noargs` method using
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the functions provided by the I18N support code:
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.. code-block:: python
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from django.core.management.base import BaseCommand, CommandError
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from django.utils import translation
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class Command(BaseCommand):
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...
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can_import_settings = True
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def handle(self, *args, **options):
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# Activate a fixed locale, e.g. Russian
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translation.activate('ru')
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# Or you can activate the LANGUAGE_CODE # chosen in the settings:
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#
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#from django.conf import settings
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#translation.activate(settings.LANGUAGE_CODE)
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# Your command logic here
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# ...
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translation.deactivate()
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Another need might be that your command simply should use the locale set in
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settings and Django should be kept from forcing it to 'en-us'. You can achieve
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it by using the :data:`BaseCommand.leave_locale_alone` option.
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When working on the scenarios described above though, take into account that
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system management commands typically have to be very careful about running in
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non-uniform locales, so you might need to:
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* Make sure the :setting:`USE_I18N` setting is always ``True`` when running
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the command (this is a good example of the potential problems stemming
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from a dynamic runtime environment that Django commands avoid offhand by
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always using a fixed locale).
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* Review the code of your command and the code it calls for behavioral
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differences when locales are changed and evaluate its impact on
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predictable behavior of your command.
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Command objects
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===============
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.. class:: BaseCommand
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The base class from which all management commands ultimately derive.
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Use this class if you want access to all of the mechanisms which
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parse the command-line arguments and work out what code to call in
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response; if you don't need to change any of that behavior,
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consider using one of its :ref:`subclasses<ref-basecommand-subclasses>`.
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Subclassing the :class:`BaseCommand` class requires that you implement the
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:meth:`~BaseCommand.handle` method.
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Attributes
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----------
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All attributes can be set in your derived class and can be used in
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:class:`BaseCommand`’s :ref:`subclasses<ref-basecommand-subclasses>`.
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.. attribute:: BaseCommand.args
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A string listing the arguments accepted by the command,
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suitable for use in help messages; e.g., a command which takes
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a list of application names might set this to '<app_label
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app_label ...>'.
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.. attribute:: BaseCommand.can_import_settings
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A boolean indicating whether the command needs to be able to
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import Django settings; if ``True``, ``execute()`` will verify
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that this is possible before proceeding. Default value is
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``True``.
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.. attribute:: BaseCommand.help
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A short description of the command, which will be printed in the
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help message when the user runs the command
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``python manage.py help <command>``.
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.. attribute:: BaseCommand.option_list
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This is the list of ``optparse`` options which will be fed
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into the command's ``OptionParser`` for parsing arguments.
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.. attribute:: BaseCommand.output_transaction
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A boolean indicating whether the command outputs SQL
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statements; if ``True``, the output will automatically be
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wrapped with ``BEGIN;`` and ``COMMIT;``. Default value is
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``False``.
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.. attribute:: BaseCommand.requires_model_validation
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A boolean; if ``True``, validation of installed models will be
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performed prior to executing the command. Default value is
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``True``. To validate an individual application's models
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rather than all applications' models, call
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:meth:`~BaseCommand.validate` from :meth:`~BaseCommand.handle`.
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.. attribute:: BaseCommand.leave_locale_alone
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A boolean indicating whether the locale set in settings should be preserved
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during the execution of the command instead of being forcibly set to 'en-us'.
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Default value is ``False``.
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Make sure you know what you are doing if you decide to change the value of
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this option in your custom command if it creates database content that
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is locale-sensitive and such content shouldn't contain any translations (like
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it happens e.g. with django.contrib.auth permissions) as making the locale
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differ from the de facto default 'en-us' might cause unintended effects. See
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the `Management commands and locales`_ section above for further details.
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This option can't be ``False`` when the
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:data:`~BaseCommand.can_import_settings` option is set to ``False`` too
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because attempting to set the locale needs access to settings. This condition
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will generate a :class:`CommandError`.
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.. versionadded:: 1.6
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The ``leave_locale_alone`` option was added in Django 1.6.
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Methods
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-------
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:class:`BaseCommand` has a few methods that can be overridden but only
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the :meth:`~BaseCommand.handle` method must be implemented.
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.. admonition:: Implementing a constructor in a subclass
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If you implement ``__init__`` in your subclass of :class:`BaseCommand`,
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you must call :class:`BaseCommand`’s ``__init__``.
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.. code-block:: python
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class Command(BaseCommand):
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def __init__(self, *args, **kwargs):
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super(Command, self).__init__(*args, **kwargs)
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# ...
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.. method:: BaseCommand.get_version()
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Return the Django version, which should be correct for all
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built-in Django commands. User-supplied commands can
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override this method to return their own version.
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.. method:: BaseCommand.execute(*args, **options)
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Try to execute this command, performing model validation if
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needed (as controlled by the attribute
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:attr:`requires_model_validation`). If the command raises a
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:class:`CommandError`, intercept it and print it sensibly to
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stderr.
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.. admonition:: Calling a management command in your code
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``execute()`` should not be called directly from your code to execute a
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command. Use :ref:`call_command <call-command>` instead.
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.. method:: BaseCommand.handle(*args, **options)
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The actual logic of the command. Subclasses must implement this method.
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.. method:: BaseCommand.validate(app=None, display_num_errors=False)
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Validates the given app, raising :class:`CommandError` for any errors.
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If ``app`` is None, then all installed apps are validated.
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.. _ref-basecommand-subclasses:
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BaseCommand subclasses
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----------------------
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.. class:: AppCommand
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A management command which takes one or more installed application labels as
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arguments, and does something with each of them.
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Rather than implementing :meth:`~BaseCommand.handle`, subclasses must
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implement :meth:`~AppCommand.handle_app_config`, which will be called once for
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each application.
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.. method:: AppCommand.handle_app_config(app_config, **options)
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Perform the command's actions for ``app_config``, which will be an
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:class:`~django.apps.AppConfig` instance corresponding to an application
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label given on the command line.
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.. versionchanged:: 1.7
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Previously, :class:`AppCommand` subclasses had to implement
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``handle_app(app, **options)`` where ``app`` was a models module. The new
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API makes it possible to handle applications without a models module. The
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fastest way to migrate is as follows::
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def handle_app_config(app_config, **options):
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if app_config.models_module is None:
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return # Or raise an exception.
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app = app_config.models_module
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# Copy the implementation of handle_app(app_config, **options) here.
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However, you may be able to simplify the implementation by using directly
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the attributes of ``app_config``.
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.. class:: LabelCommand
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A management command which takes one or more arbitrary arguments
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(labels) on the command line, and does something with each of
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them.
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Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement
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:meth:`~LabelCommand.handle_label`, which will be called once for each label.
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.. method:: LabelCommand.handle_label(label, **options)
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Perform the command's actions for ``label``, which will be the
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string as given on the command line.
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.. class:: NoArgsCommand
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A command which takes no arguments on the command line.
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Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement
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:meth:`~NoArgsCommand.handle_noargs`; :meth:`~BaseCommand.handle` itself is
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overridden to ensure no arguments are passed to the command.
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.. method:: NoArgsCommand.handle_noargs(**options)
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Perform this command's actions
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.. _ref-command-exceptions:
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Command exceptions
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------------------
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.. class:: CommandError
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Exception class indicating a problem while executing a management
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command.
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If this exception is raised during the execution of a management
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command from a command line console, it will be caught and turned into a
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nicely-printed error message to the appropriate output stream (i.e., stderr);
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as a result, raising this exception (with a sensible description of the
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error) is the preferred way to indicate that something has gone
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wrong in the execution of a command.
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If a management command is called from code through
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:ref:`call_command <call-command>`, it's up to you to catch the exception
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when needed.
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