Custom Management Commands

7/25/2019 Custom Management Commands

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====================================Writing custom django-admin commands====================================

.. module:: django.core.management

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'redistributing. In this document, we will be building a custom ``closepoll``command for the ``polls`` application from the:doc:`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 thatdirectory 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

In this example, the ``closepoll`` command will be made available to any projectthat includes the ``polls`` application in :setting:`INSTALLED_APPS`.

The ``_private.py`` module will not be available as a management command.

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

.. admonition:: Standalone scripts

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`` tolook like this:

.. code-block:: python

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

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

def handle(self, *args, **options): for poll_id in args: try: poll = Poll.objects.get(pk=int(poll_id)) except Poll.DoesNotExist:


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raise CommandError('Poll "%s" does not exist' % poll_id)

poll.opened = False poll.save()

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

.. _management-commands-output:

.. note:: 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``.

The ``handle()`` method takes zero or more ``poll_ids`` and sets ``poll.opened``

to ``False`` for each one. If the user referenced any nonexistent polls, a:class:`CommandError` is raised. The ``poll.opened`` attribute does not existin the :doc:`tutorial` and was added to``polls.models.Poll`` for this example.

The same ``closepoll`` could be easily modified to delete a given poll insteadof closing it by accepting additional command line options. These custom optionsmust be added to :attr:`~BaseCommand.option_list` like this:


from optparse import make_option

class Command(BaseCommand): option_list = BaseCommand.option_list + ( make_option('--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 dictparameter of the handle method. See the :py:mod:`optparse` Python documentationfor more about ``make_option`` usage.

In addition to being able to add custom command line options, all:doc:`management commands` can accept somedefault options such as :djadminopt:`--verbosity` and :djadminopt:`--traceback`.


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.. admonition:: Management commands and locales

The :meth:`BaseCommand.execute` method sets the hardcoded `èn-us`` locale because the commands shipped with Django perform several tasks (for example, user-facing content rendering and database population) that require a system-neutral string language (for which we use `èn-us``).

If your custom management command uses another locale, you should manually activate and deactivate it in your :meth:`~BaseCommand.handle` or :meth:`~NoArgsCommand.handle_noargs` 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()

Take into account though, that system management commands typically have to be very careful about running in non-uniform locales, so:

* Make sure the :setting:ÙSE_I18N` setting is always ``True`` when running the command (this is one good example of the potential problems stemming from a dynamic runtime environment that Django commands avoid offhand by always using a fixed locale).

* 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.

Command objects

===============

.. class:: BaseCommand

The base class from which all management commands ultimately derive.

Use this class if you want access to all of the mechanisms whichparse the command-line arguments and work out what code to call inresponse; if you don't need to change any of that behavior,consider using one of its :ref:`subclasses`.


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Subclassing the :class:`BaseCommand` class requires that you implement the:meth:`~BaseCommand.handle` method.

Attributes----------

All attributes can be set in your derived class and can be used in:class:`BaseCommand`'s :ref:`subclasses`.

.. attribute:: BaseCommand.args

A string listing the arguments accepted by the command, suitable for use in help messages; e.g., a command which takes a list of application names might set this to ''.

.. attribute:: BaseCommand.can_import_settings

A boolean indicating whether the command needs to be able to import Django settings; if ``True``, `èxecute()`` will verify that this is possible before proceeding. Default value is ``True``.

.. attribute:: BaseCommand.help

A short description of the command, which will be printed in the help message when the user runs the command ``python manage.py help ``.

.. attribute:: BaseCommand.option_list

This is the list of `òptparse`` options which will be fed into the command's `ÒptionParser`` for parsing arguments.

.. attribute:: 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``.

.. attribute:: BaseCommand.requires_model_validation

A boolean; if ``True``, validation of installed models will be performed prior to executing the command. Default value is ``True``. To validate an individual application's models rather than all applications' models, call :meth:`~BaseCommand.validate` from :meth:`~BaseCommand.handle`.

Methods-------

:class:`BaseCommand` has a few methods that can be overridden but onlythe :meth:`~BaseCommand.handle` method must be implemented.

.. admonition:: Implementing a constructor in a subclass

If you implement ``__init__`` in your subclass of :class:`BaseCommand`, you must call :class:`BaseCommand`'s ``__init__``.


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class Command(BaseCommand): def __init__(self, *args, **kwargs): super(Command, self).__init__(*args, **kwargs) # ...

.. method:: BaseCommand.get_version()

Return 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.

.. method:: BaseCommand.execute(*args, **options)

Try to execute this command, performing model validation if needed (as controlled by the attribute :attr:`requires_model_validation`). If the command raises a :class:`CommandError`, intercept it and print it sensibly to stderr.

.. admonition:: Calling a management command in your code

`èxecute()`` should not be called directly from your code to execute a command. Use :ref:`call_command ` instead.

.. method:: BaseCommand.handle(*args, **options)

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

.. method:: BaseCommand.validate(app=None, display_num_errors=False)

Validates the given app, raising :class:`CommandError` for any errors.

If `àpp`` is None, then all installed apps are validated.

.. _ref-basecommand-subclasses:

BaseCommand subclasses----------------------

.. class:: AppCommand

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

Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement:meth:`~AppCommand.handle_app`, which will be called once for each application.

.. method:: AppCommand.handle_app(app, **options)

Perform the command's actions for `àpp``, which will be the Python module corresponding to an application name given on the command line.

.. class:: LabelCommand

A management command which takes one or more arbitrary arguments


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(labels) on the command line, and does something with each ofthem.

Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement:meth:`~LabelCommand.handle_label`, which will be called once for each label.

.. method:: LabelCommand.handle_label(label, **options)

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

.. class:: NoArgsCommand

A command which takes no arguments on the command line.

Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement:meth:`~NoArgsCommand.handle_noargs`; :meth:`~BaseCommand.handle` itself isoverridden to ensure no arguments are passed to the command.

.. method:: NoArgsCommand.handle_noargs(**options)

Perform this command's actions

.. _ref-command-exceptions:

Command exceptions------------------

.. class:: CommandError

Exception class indicating a problem while executing a managementcommand.

If this exception is raised during the execution of a managementcommand from a command line console, it will be caught and turned into anicely-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 gonewrong in the execution of a command.

If a management command is called from code through:ref:`call_command `, it's up to you to catch the exceptionwhen needed.

Documents

Custom Management Commands