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:
polls/ __init__.py models.py management/ __init__.py commands/ __init__.py _private.py closepoll.py tests.py views.py
On Python 2, be sure to include __init__.py files in both the management and management/commands directories as done above or your command will not be detected.
In this example, the closepoll command will be made available to any project that includes the polls application in INSTALLED_APPS.
The _private.py module will not be available as a management command.
Custom management commands are especially useful for running standalone scripts or for scripts that are periodically executed from the UNIX crontab or from Windows scheduled tasks control panel.
To implement the command, edit polls/management/commands/closepoll.py to look like this:
from django.core.management.base import BaseCommand, CommandError from polls.models import 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('Successfully closed poll "%s"' % poll_id)
When you are using management commands and wish to provide console output, you should write to self.stdout and self.stderr, instead of printing to stdout and stderr directly. By using these proxies, it becomes much easier to test your custom command. Note also that you don’t need to end messages with a newline character, it will be added automatically, unless you specify the ending parameter:
self.stdout.write("Unterminated line", ending='')
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.Poll for this example.
Accepting optional arguments¶
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:
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', default=False, 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.
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:
from django.core.management.base import BaseCommand, CommandError from django.utils import translation class Command(BaseCommand): ... can_import_settings = True 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.
- 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.
A boolean indicating whether the command needs to be able to import Django settings; if True, execute() will verify that this is possible before proceeding. Default value is True.
A short description of the command, which will be printed in the help message when the user runs the command python manage.py help <command>.
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”).
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.
A boolean; if True, the entire Django project will be checked for potential problems prior to executing the command. Default value is True.
A boolean indicating whether the locale set in settings should be preserved during the execution of the command instead of being forcibly set to ‘en-us’.
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 making the locale differ from the de facto default ‘en-us’ might cause unintended effects. Seethe Management commands and locales section above for further details.
Implementing a constructor in a subclass
class Command(BaseCommand): def __init__(self, *args, **kwargs): super(Command, self).__init__(*args, **kwargs) # ...
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.
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.
Calling a management command in your code
execute() should not be called directly from your code to execute a command. Use call_command instead.
- BaseCommand.handle(*args, **options)¶
The actual logic of the command. Subclasses must implement this method.
It may return a Unicode 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.
- class AppCommand¶
A management command which takes one or more installed application labels as arguments, and does something with each of them.
- 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.
- LabelCommand.handle_label(label, **options)¶
Perform the command’s actions for label, which will be the string as given on the command line.
- class 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.