393 lines
15 KiB
Plaintext
393 lines
15 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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from django.core.management.base import BaseCommand, CommandError
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from polls.models import Question as Poll
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class Command(BaseCommand):
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help = 'Closes the specified poll for voting'
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def add_arguments(self, parser):
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parser.add_argument('poll_id', nargs='+', type=int)
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def handle(self, *args, **options):
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for poll_id in options['poll_id']:
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try:
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poll = Poll.objects.get(pk=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(self.style.SUCCESS('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 one 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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:exc:`CommandError` is raised. The ``poll.opened`` attribute does not exist in
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the :doc:`tutorial</intro/tutorial01>` and was added to
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``polls.models.Question`` for this example.
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.. _custom-commands-options:
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Accepting optional arguments
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============================
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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
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options can be added in the :meth:`~BaseCommand.add_arguments` method like this::
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class Command(BaseCommand):
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def add_arguments(self, parser):
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# Positional arguments
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parser.add_argument('poll_id', nargs='+', type=int)
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# Named (optional) arguments
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parser.add_argument(
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'--delete',
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action='store_true',
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dest='delete',
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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:`argparse` Python documentation
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for more about ``add_argument`` 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 default options
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such as :option:`--verbosity` and :option:`--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 deactivates translations
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because some commands shipped with Django perform several tasks (for example,
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user-facing content rendering and database population) that require a
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project-neutral string language.
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If, for some reason, your custom management command needs to use a fixed locale,
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you should manually activate and deactivate it in your
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:meth:`~BaseCommand.handle` method using the functions provided by the I18N
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support code::
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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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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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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 deactivating it. 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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deactivating translations).
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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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Testing
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=======
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Information on how to test custom management commands can be found in the
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:ref:`testing docs <topics-testing-management-commands>`.
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Overriding commands
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===================
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Django registers the built-in commands and then searches for commands in
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:setting:`INSTALLED_APPS` in reverse. During the search, if a command name
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duplicates an already registered command, the newly discovered command
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overrides the first.
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In other words, to override a command, the new command must have the same name
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and its app must be before the overridden command's app in
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:setting:`INSTALLED_APPS`.
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Management commands from third-party apps that have been unintentionally
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overridden can be made available under a new name by creating a new command in
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one of your project's apps (ordered before the third-party app in
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:setting:`INSTALLED_APPS`) which imports the ``Command`` of the overridden
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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.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.missing_args_message
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If your command defines mandatory positional arguments, you can customize
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the message error returned in the case of missing arguments. The default is
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output by :py:mod:`argparse` ("too few arguments").
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.. attribute:: BaseCommand.output_transaction
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A boolean indicating whether the command outputs SQL statements; if
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``True``, the output will automatically be wrapped with ``BEGIN;`` and
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``COMMIT;``. Default value is ``False``.
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.. attribute:: BaseCommand.requires_migrations_checks
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A boolean; if ``True``, the command prints a warning if the set of
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migrations on disk don't match the migrations in the database. A warning
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doesn't prevent the command from executing. Default value is ``False``.
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.. attribute:: BaseCommand.requires_system_checks
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A boolean; if ``True``, the entire Django project will be checked for
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potential problems prior to executing the command. Default value is ``True``.
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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
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(like it happens e.g. with :mod:`django.contrib.auth` permissions) as
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making the locale differ from the de facto default 'en-us' might cause
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unintended effects. See the `Management commands and locales`_ section
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above for further details.
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.. attribute:: BaseCommand.style
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An instance attribute that helps create colored output when writing to
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``stdout`` or ``stderr``. For example::
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self.stdout.write(self.style.SUCCESS('...'))
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See :ref:`syntax-coloring` to learn how to modify the color palette and to
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see the available styles (use uppercased versions of the "roles" described
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in that section).
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If you pass the :option:`--no-color` option when running your command, all
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``self.style()`` calls will return the original string uncolored.
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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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class Command(BaseCommand):
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def __init__(self, *args, **kwargs):
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super().__init__(*args, **kwargs)
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# ...
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.. method:: BaseCommand.add_arguments(parser)
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Entry point to add parser arguments to handle command line arguments passed
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to the command. Custom commands should override this method to add both
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positional and optional arguments accepted by the command. Calling
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``super()`` is not needed when directly subclassing ``BaseCommand``.
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.. method:: BaseCommand.get_version()
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Returns the Django version, which should be correct for all built-in Django
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commands. User-supplied commands can override this method to return their
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own version.
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.. method:: BaseCommand.execute(*args, **options)
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Tries to execute this command, performing system checks if needed (as
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controlled by the :attr:`requires_system_checks` attribute). If the command
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raises a :exc:`CommandError`, it's intercepted and printed to 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 :func:`~django.core.management.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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It may return a string which will be printed to ``stdout`` (wrapped
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by ``BEGIN;`` and ``COMMIT;`` if :attr:`output_transaction` is ``True``).
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.. method:: BaseCommand.check(app_configs=None, tags=None, display_num_errors=False)
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Uses the system check framework to inspect the entire Django project for
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potential problems. Serious problems are raised as a :exc:`CommandError`;
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warnings are output to stderr; minor notifications are output to stdout.
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If ``app_configs`` and ``tags`` are both ``None``, all system checks are
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performed. ``tags`` can be a list of check tags, like ``compatibility`` or
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``models``.
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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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.. class:: LabelCommand
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A management command which takes one or more arbitrary arguments (labels) on
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the command line, and does something with each of 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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.. attribute:: LabelCommand.label
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A string describing the arbitrary arguments passed to the command. The
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string is used in the usage text and error messages of the command.
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Defaults to ``'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 string as
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given on the command line.
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Command exceptions
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------------------
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.. exception:: CommandError
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Exception class indicating a problem while executing a management command.
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If this exception is raised during the execution of a management command from a
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command line console, it will be caught and turned into a nicely-printed error
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message to the appropriate output stream (i.e., stderr); as a result, raising
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this exception (with a sensible description of the error) is the preferred way
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to indicate that something has gone wrong in the execution of a command.
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If a management command is called from code through
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:func:`~django.core.management.call_command`, it's up to you to catch the
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exception when needed.
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