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
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.
The closepoll.py
module has only one requirement – it must define a class
Command
that extends BaseCommand
or one of its
subclasses.
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
to
look like this:
from django.core.management.base import BaseCommand, CommandError
from polls.models import Poll
class Command(BaseCommand):
args = '<poll_id poll_id ...>'
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:
raise CommandError('Poll "%s" does not exist' % poll_id)
poll.opened = False
poll.save()
self.stdout.write('Successfully closed poll "%s"' % poll_id)
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
<poll_id>
.
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
CommandError
is raised. The poll.opened
attribute does not exist
in the tutorial and was added to
polls.models.Poll
for this example.
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
must be added to 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 dict
parameter of the handle method. See the optparse
Python documentation
for more about make_option
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
The BaseCommand.execute()
method sets the hardcoded en-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 en-us
).
If your custom management command uses another locale, you should manually
activate and deactivate it in your handle()
or
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
USE_I18N
setting is alwaysTrue
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 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.
Attributes¶
All attributes can be set in your derived class and can be used in
BaseCommand
‘s subclasses.
-
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 ‘<appname appname ...>’.
-
BaseCommand.
can_import_settings
¶ 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 isTrue
.
-
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 <command>
.
-
BaseCommand.
option_list
¶ This is the list of
optparse
options which will be fed into the command’sOptionParser
for parsing arguments.
-
BaseCommand.
output_transaction
¶ A boolean indicating whether the command outputs SQL statements; if
True
, the output will automatically be wrapped withBEGIN;
andCOMMIT;
. Default value isFalse
.
-
BaseCommand.
requires_model_validation
¶ A boolean; if
True
, validation of installed models will be performed prior to executing the command. Default value isTrue
. To validate an individual application’s models rather than all applications’ models, callvalidate()
fromhandle()
.
Methods¶
BaseCommand
has a few methods that can be overridden but only
the handle()
method must be implemented.
Implementing a constructor in a subclass
If you implement __init__
in your subclass of BaseCommand
,
you must call BaseCommand
‘s __init__
.
class Command(BaseCommand):
def __init__(self, *args, **kwargs):
super(Command, self).__init__(*args, **kwargs)
# ...
-
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.
-
BaseCommand.
execute
(*args, **options)¶ Try to execute this command, performing model validation if needed (as controlled by the attribute
requires_model_validation
). If the command raises aCommandError
, intercept it and print it sensibly 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.
-
BaseCommand.
validate
(app=None, display_num_errors=False)¶ Validates the given app, raising
CommandError
for any errors.If
app
is None, then all installed apps are validated.
BaseCommand subclasses¶
-
class
AppCommand
¶
A management command which takes one or more installed application names as arguments, and does something with each of them.
Rather than implementing handle()
, subclasses must implement
handle_app()
, which will be called once for each application.
-
AppCommand.
handle_app
(app, **options)¶ Perform the command’s actions for
app
, 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 (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.
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 handle()
, subclasses must implement
handle_noargs()
; handle()
itself is
overridden to ensure no arguments are passed to the command.
-
NoArgsCommand.
handle_noargs
(**options)¶ Perform this command’s actions
Command exceptions¶
-
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.