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Writing custom django-admin commands

Applications can register their own actions with manage.py. For example, you might want to add a manage.py action for a Django app that you’re distributing. In this document, we will be building a custom closepoll command for the polls application from the tutorial.

To do this, just add a management/commands directory to the application. Django will register a manage.py command for each Python module in that directory whose name doesn’t begin with an underscore. For example:

Code
polls/
    __init__.py
    models.py
    management/
        __init__.py
        commands/
            __init__.py
            _private.py
            closepoll.py
    tests.py
    views.py

In this example, the closepoll command will be made available to any project that includes the polls application in INSTALLED_APPS.

El módulo _private.py no estará disponible como comando de administración.

The closepoll.py module has only one requirement – it must define a class Command that extends BaseCommand or one of its subclasses.

Para implementar el comando, edite polls/management/commands/closepoll.py para que se parezca a:

Code
from django.core.management.base import BaseCommand, CommandError
from polls.models import Question as Poll

class Command(BaseCommand):
    help = 'Closes the specified poll for voting'

    def add_arguments(self, parser):
        parser.add_argument('poll_id', nargs='+', type=int)

    def handle(self, *args, **options):
        for poll_id in options['poll_id']:
            try:
                poll = Poll.objects.get(pk=poll_id)
            except Poll.DoesNotExist:
                raise CommandError('Poll "%s" does not exist' % poll_id)

            poll.opened = False
            poll.save()

            self.stdout.write(self.style.SUCCESS('Successfully closed poll "%s"' % poll_id))

The new custom command can be called using python manage.py closepoll <poll_id>.

The handle() method takes one or more poll_ids and sets poll.opened to False for each one. If the user referenced any nonexistent polls, a CommandError is raised. The poll.opened attribute does not exist in the tutorial and was added to polls.models.Question for this example.

Aceptar los argumentos opcionales

The same closepoll could be easily modified to delete a given poll instead of closing it by accepting additional command line options. These custom options can be added in the add_arguments() method like this:

Code
class Command(BaseCommand):
    def add_arguments(self, parser):
        # Positional arguments
        parser.add_argument('poll_id', nargs='+', type=int)

        # Named (optional) arguments
        parser.add_argument(
            '--delete',
            action='store_true',
            dest='delete',
            help='Delete poll instead of closing it',
        )

    def handle(self, *args, **options):
        # ...
        if options['delete']:
            poll.delete()
        # ...

The option (delete in our example) is available in the options dict parameter of the handle method. See the argparse Python documentation for more about add_argument usage.

In addition to being able to add custom command line options, all management commands can accept some default options such as --verbosity and --traceback.

Management commands and locales

By default, the BaseCommand.execute() method deactivates translations because some commands shipped with Django perform several tasks (for example, user-facing content rendering and database population) that require a project-neutral string language.

If, for some reason, your custom management command needs to use a fixed locale, you should manually activate and deactivate it in your handle() method using the functions provided by the I18N support code:

Code
from django.core.management.base import BaseCommand, CommandError
from django.utils import translation

class Command(BaseCommand):
    ...

    def handle(self, *args, **options):

        # Activate a fixed locale, e.g. Russian
        translation.activate('ru')

        # Or you can activate the LANGUAGE_CODE # chosen in the settings:
        from django.conf import settings
        translation.activate(settings.LANGUAGE_CODE)

        # Your command logic here
        ...

        translation.deactivate()

Another need might be that your command simply should use the locale set in settings and Django should be kept from deactivating it. You can achieve it by using the BaseCommand.leave_locale_alone option.

When working on the scenarios described above though, take into account that system management commands typically have to be very careful about running in non-uniform locales, so you might need to:

  • Make sure the USE_I18N setting is always True when running the command (this is a good example of the potential problems stemming from a dynamic runtime environment that Django commands avoid offhand by deactivating translations).

  • Review the code of your command and the code it calls for behavioral differences when locales are changed and evaluate its impact on predictable behavior of your command.

Testing

Information on how to test custom management commands can be found in the testing docs.

Overriding commands

Django registers the built-in commands and then searches for commands in INSTALLED_APPS in reverse. During the search, if a command name duplicates an already registered command, the newly discovered command overrides the first.

In other words, to override a command, the new command must have the same name and its app must be before the overridden command’s app in INSTALLED_APPS.

Management commands from third-party apps that have been unintentionally overridden can be made available under a new name by creating a new command in one of your project’s apps (ordered before the third-party app in INSTALLED_APPS) which imports the Command of the overridden command.

Objetos de Comando

class BaseCommand

The base class from which all management commands ultimately derive.

Use this class if you want access to all of the mechanisms which parse the command-line arguments and work out what code to call in response; if you don’t need to change any of that behavior, consider using one of its subclasses.

Subclassing the BaseCommand class requires that you implement the handle() method.

Atributos

All attributes can be set in your derived class and can be used in BaseCommand’s subclasses.

BaseCommand.help

Una breve descripción del comando que será imprimida en el mensaje de ayuda cuando el usuario ejecute python manage.py help <comando>.

BaseCommand.missing_args_message

If your command defines mandatory positional arguments, you can customize the message error returned in the case of missing arguments. The default is output by argparse («too few arguments»).

BaseCommand.output_transaction

A boolean indicating whether the command outputs SQL statements; if True, the output will automatically be wrapped with BEGIN; and COMMIT;. Default value is False.

BaseCommand.requires_migrations_checks

A boolean; if True, the command prints a warning if the set of migrations on disk don’t match the migrations in the database. A warning doesn’t prevent the command from executing. Default value is False.

BaseCommand.requires_system_checks

A boolean; if True, the entire Django project will be checked for potential problems prior to executing the command. Default value is True.

BaseCommand.leave_locale_alone

A boolean indicating whether the locale set in settings should be preserved during the execution of the command instead of translations being deactivated.

Default value is False.

Make sure you know what you are doing if you decide to change the value of this option in your custom command if it creates database content that is locale-sensitive and such content shouldn’t contain any translations (like it happens e.g. with django.contrib.auth permissions) as activating any locale might cause unintended effects. See the Management commands and locales section above for further details.

BaseCommand.style

An instance attribute that helps create colored output when writing to stdout or stderr. For example:

Code
self.stdout.write(self.style.SUCCESS('...'))

See Syntax coloring to learn how to modify the color palette and to see the available styles (use uppercased versions of the «roles» described in that section).

If you pass the --no-color option when running your command, all self.style() calls will return the original string uncolored.

Métodos

BaseCommand has a few methods that can be overridden but only the handle() method must be implemented.

BaseCommand.add_arguments(parser)

Entry point to add parser arguments to handle command line arguments passed to the command. Custom commands should override this method to add both positional and optional arguments accepted by the command. Calling super() is not needed when directly subclassing BaseCommand.

BaseCommand.get_version()

Returns the Django version, which should be correct for all built-in Django commands. User-supplied commands can override this method to return their own version.

BaseCommand.execute(*args, **options)

Tries to execute this command, performing system checks if needed (as controlled by the requires_system_checks attribute). If the command raises a CommandError, it’s intercepted and printed to stderr.

BaseCommand.handle(*args, **options)

The actual logic of the command. Subclasses must implement this method.

It may return a string which will be printed to stdout (wrapped by BEGIN; and COMMIT; if output_transaction is True).

BaseCommand.check(app_configs=None, tags=None, display_num_errors=False)

Uses the system check framework to inspect the entire Django project for potential problems. Serious problems are raised as a CommandError; warnings are output to stderr; minor notifications are output to stdout.

If app_configs and tags are both None, all system checks are performed. tags can be a list of check tags, like compatibility or models.

BaseCommand subclasses

class AppCommand

A management command which takes one or more installed application labels as arguments, and does something with each of them.

Rather than implementing handle(), subclasses must implement handle_app_config(), which will be called once for each application.

AppCommand.handle_app_config(app_config, **options)

Perform the command’s actions for app_config, which will be an AppConfig instance corresponding to an application label given on the command line.

class LabelCommand

A management command which takes one or more arbitrary arguments (labels) on the command line, and does something with each of them.

Rather than implementing handle(), subclasses must implement handle_label(), which will be called once for each label.

LabelCommand.label

A string describing the arbitrary arguments passed to the command. The string is used in the usage text and error messages of the command. Defaults to 'label'.

LabelCommand.handle_label(label, **options)

Perform the command’s actions for label, which will be the string as given on the command line.

Excepciones de comando

exception CommandError

Exception class indicating a problem while executing a management command.

If this exception is raised during the execution of a management command from a command line console, it will be caught and turned into a nicely-printed error message to the appropriate output stream (i.e., stderr); as a result, raising this exception (with a sensible description of the error) is the preferred way to indicate that something has gone wrong in the execution of a command.

If a management command is called from code through call_command(), it’s up to you to catch the exception when needed.

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