Writing customdjango-admin commands¶
Applications can register their own actions withmanage.py. For example,you might want to add amanage.py action for a Django app that you’redistributing. In this document, we will be building a customclosepollcommand for thepolls application from thetutorial.
To do this, just add amanagement/commands directory to the application.Django will register amanage.py command for each Python module in thatdirectory whose name doesn’t begin with an underscore. For example:
polls/__init__.pymodels.pymanagement/commands/_private.pyclosepoll.pytests.pyviews.py
In this example, theclosepoll command will be made available to any projectthat includes thepolls application inINSTALLED_APPS.
The_private.py module will not be available as a management command.
Theclosepoll.py module has only one requirement – it must define a classCommand that extendsBaseCommand or one of itssubclasses.
Standalone scripts
Custom management commands are especially useful for running standalonescripts or for scripts that are periodically executed from the UNIX crontabor from Windows scheduled tasks control panel.
To implement the command, editpolls/management/commands/closepoll.py tolook like this:
fromdjango.core.management.baseimportBaseCommand,CommandErrorfrompolls.modelsimportQuestionasPollclassCommand(BaseCommand):help='Closes the specified poll for voting'defadd_arguments(self,parser):parser.add_argument('poll_id',nargs='+',type=int)defhandle(self,*args,**options):forpoll_idinoptions['poll_id']:try:poll=Poll.objects.get(pk=poll_id)exceptPoll.DoesNotExist:raiseCommandError('Poll "%s" does not exist'%poll_id)poll.opened=Falsepoll.save()self.stdout.write(self.style.SUCCESS('Successfully closed poll "%s"'%poll_id))
Note
When you are using management commands and wish to provide consoleoutput, you should write toself.stdout andself.stderr,instead of printing tostdout andstderr directly. Byusing these proxies, it becomes much easier to test your customcommand. Note also that you don’t need to end messages with a newlinecharacter, it will be added automatically, unless you specify theendingparameter:
self.stdout.write("Unterminated line",ending='')
The new custom command can be called usingpythonmanage.pyclosepoll<poll_id>.
Thehandle() method takes one or morepoll_ids and setspoll.openedtoFalse for each one. If the user referenced any nonexistent polls, aCommandError is raised. Thepoll.opened attribute does not exist inthetutorial and was added topolls.models.Question for this example.
Accepting optional arguments¶
The sameclosepoll could be easily modified to delete a given poll insteadof closing it by accepting additional command line options. These customoptions can be added in theadd_arguments() method like this:
classCommand(BaseCommand):defadd_arguments(self,parser):# Positional argumentsparser.add_argument('poll_id',nargs='+',type=int)# Named (optional) argumentsparser.add_argument('--delete',action='store_true',dest='delete',help='Delete poll instead of closing it',)defhandle(self,*args,**options):# ...ifoptions['delete']:poll.delete()# ...
The option (delete in our example) is available in the options dictparameter of the handle method. See theargparse Python documentationfor more aboutadd_argument usage.
In addition to being able to add custom command line options, allmanagement commands can accept some default optionssuch as--verbosity and--traceback.
Management commands and locales¶
By default, management commands are executed with the current active locale.
If, for some reason, your custom management command must run without an activelocale (for example, to prevent translated content from being inserted intothe database), deactivate translations using the@no_translationsdecorator on yourhandle() method:
fromdjango.core.management.baseimportBaseCommand,no_translationsclassCommand(BaseCommand):...@no_translationsdefhandle(self,*args,**options):...
Since translation deactivation requires access to configured settings, thedecorator can’t be used for commands that work without configured settings.
The@no_translations decorator is new. In older versions, translationsare deactivated before running a command unless the command’sleave_locale_alone attribute (now removed) is set toTrue.
Testing¶
Information on how to test custom management commands can be found in thetesting docs.
Overriding commands¶
Django registers the built-in commands and then searches for commands inINSTALLED_APPS in reverse. During the search, if a command nameduplicates an already registered command, the newly discovered commandoverrides the first.
In other words, to override a command, the new command must have the same nameand its app must be before the overridden command’s app inINSTALLED_APPS.
Management commands from third-party apps that have been unintentionallyoverridden can be made available under a new name by creating a new command inone of your project’s apps (ordered before the third-party app inINSTALLED_APPS) which imports theCommand of the overriddencommand.
Command objects¶
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 itssubclasses.
Subclassing theBaseCommand class requires that you implement thehandle() method.
Attributes¶
All attributes can be set in your derived class and can be used inBaseCommand’ssubclasses.
BaseCommand.help¶A short description of the command, which will be printed in thehelp message when the user runs the command
pythonmanage.pyhelp<command>.
BaseCommand.missing_args_message¶If your command defines mandatory positional arguments, you can customizethe message error returned in the case of missing arguments. The default isoutput 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 withBEGIN;andCOMMIT;. Default value isFalse.
BaseCommand.requires_migrations_checks¶A boolean; if
True, the command prints a warning if the set ofmigrations on disk don’t match the migrations in the database. A warningdoesn’t prevent the command from executing. Default value isFalse.
BaseCommand.requires_system_checks¶A boolean; if
True, the entire Django project will be checked forpotential problems prior to executing the command. Default value isTrue.
BaseCommand.style¶An instance attribute that helps create colored output when writing to
stdoutorstderr. For example:self.stdout.write(self.style.SUCCESS('...'))
SeeSyntax coloring to learn how to modify the color palette and tosee the available styles (use uppercased versions of the “roles” describedin that section).
If you pass the
--no-coloroption when running your command, allself.style()calls will return the original string uncolored.
Methods¶
BaseCommand has a few methods that can be overridden but onlythehandle() method must be implemented.
Implementing a constructor in a subclass
If you implement__init__ in your subclass ofBaseCommand,you must callBaseCommand’s__init__:
classCommand(BaseCommand):def__init__(self,*args,**kwargs):super().__init__(*args,**kwargs)# ...
BaseCommand.add_arguments(parser)[source]¶Entry point to add parser arguments to handle command line arguments passedto the command. Custom commands should override this method to add bothpositional and optional arguments accepted by the command. Calling
super()is not needed when directly subclassingBaseCommand.
BaseCommand.get_version()[source]¶Returns the Django version, which should be correct for all built-in Djangocommands. User-supplied commands can override this method to return theirown version.
BaseCommand.execute(*args,**options)[source]¶Tries to execute this command, performing system checks if needed (ascontrolled by the
requires_system_checksattribute). If the commandraises aCommandError, 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 acommand. Usecall_command() instead.
BaseCommand.handle(*args,**options)[source]¶The actual logic of the command. Subclasses must implement this method.
It may return a string which will be printed to
stdout(wrappedbyBEGIN;andCOMMIT;ifoutput_transactionisTrue).
BaseCommand.check(app_configs=None,tags=None,display_num_errors=False)[source]¶Uses the system check framework to inspect the entire Django project forpotential problems. Serious problems are raised as a
CommandError;warnings are output to stderr; minor notifications are output to stdout.If
app_configsandtagsare bothNone, all system checks areperformed.tagscan be a list of check tags, likecompatibilityormodels.
BaseCommand subclasses¶
- class
AppCommand¶
A management command which takes one or more installed application labels asarguments, and does something with each of them.
Rather than implementinghandle(), subclasses mustimplementhandle_app_config(), which will be called once foreach application.
AppCommand.handle_app_config(app_config,**options)¶Perform the command’s actions for
app_config, which will be anAppConfiginstance corresponding to an applicationlabel given on the command line.
- class
LabelCommand¶
A management command which takes one or more arbitrary arguments (labels) onthe command line, and does something with each of them.
Rather than implementinghandle(), subclasses must implementhandle_label(), which will be called once for each label.
LabelCommand.label¶A string describing the arbitrary arguments passed to the command. Thestring 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 asgiven on the command line.
Command exceptions¶
Exception class indicating a problem while executing a management command.
If this exception is raised during the execution of a management command from acommand line console, it will be caught and turned into a nicely-printed errormessage to the appropriate output stream (i.e., stderr); as a result, raisingthis exception (with a sensible description of the error) is the preferred wayto indicate that something has gone wrong in the execution of a command.
If a management command is called from code throughcall_command(), it’s up to you to catch theexception when needed.
