应用可以使用manage.py注册自己的动作，例如，你可能想要为你即将发布的应用添加一个manage.py 操作。这节我们将为polls应用添加一个closepoll的命令
添加一个management/commands目录如下
polls/
__init__.py
models.py
management/
__init__.py
commands/
__init__.py
_private.py
closepoll.py
tests.py
views.py
这样添加之后，任何包含polls在INSTALLED_APPS的项目都可以使用closepoll命令
_private.py模块不会作为一个管理命令
closepoll.py模块有一个要求--必须定义一个类Command拓展或者继承BaseCommand
下面是这个命令的一个实例实现（closepoll.py）
from django.core.management.base import BaseCommand, CommandError
from example.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"\n' % poll_id)
注意：使用self.stdout和self.stderr而不是stdout和stderr
这个新命令的可以通过python manage.py closepoll <poll_id>来调用
更多更详细的关于BaseCommand的代码附于下面：常用到的参数是args（参数格式说明）和help（命令说明），必须实现的方法是handle（如何实现这个命令），正如上面的例子的那样，如果没有特别的要求，下面的代码其实不用看了。
class BaseCommand(object):
"""
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 the subclasses defined in this file.
If you are interested in overriding/customizing various aspects of
the command-parsing and -execution behavior, the normal flow works
as follows:
1. ``django-admin.py`` or ``manage.py`` loads the command class
and calls its ``run_from_argv()`` method.
2. The ``run_from_argv()`` method calls ``create_parser()`` to get
an ``OptionParser`` for the arguments, parses them, performs
any environment changes requested by options like
``pythonpath``, and then calls the ``execute()`` method,
passing the parsed arguments.
3. The ``execute()`` method attempts to carry out the command by
calling the ``handle()`` method with the parsed arguments; any
output produced by ``handle()`` will be printed to standard
output and, if the command is intended to produce a block of
SQL statements, will be wrapped in ``BEGIN`` and ``COMMIT``.
4. If ``handle()`` raised a ``CommandError``, ``execute()`` will
instead print an error message to ``stderr``.
Thus, the ``handle()`` method is typically the starting point for
subclasses; many built-in commands and command types either place
all of their logic in ``handle()``, or perform some additional
parsing work in ``handle()`` and then delegate from it to more
specialized methods as needed.
Several attributes affect behavior at various steps along the way:
``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 ...>'.
``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 is
``True``.
``help``
A short description of the command, which will be printed in
help messages.
``option_list``
This is the list of ``optparse`` options which will be fed
into the command's ``OptionParser`` for parsing arguments.
``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``.
``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
``self.validate(app)`` from ``handle()``, where ``app`` is the
application's Python module.
"""
# Metadata about this command.
option_list = (
make_option('-v', '--verbosity', action='store', dest='verbosity', default='1',
type='choice', choices=['0', '1', '2', '3'],
help='Verbosity level; 0=minimal output, 1=normal output, 2=verbose output, 3=very verbose output'),
make_option('--settings',
help='The Python path to a settings module, e.g. "myproject.settings.main". If this isn\'t provided, the DJANGO_SETTINGS_MODULE environment variable will be used.'),
make_option('--pythonpath',
help='A directory to add to the Python path, e.g. "/home/djangoprojects/myproject".'),
make_option('--traceback', action='store_true',
help='Print traceback on exception'),
)
help = ''
args = ''
# Configuration shortcuts that alter various logic.
can_import_settings = True
requires_model_validation = True
output_transaction = False # Whether to wrap the output in a "BEGIN; COMMIT;"
def __init__(self):
self.style = color_style()
def get_version(self):
"""
Return the Django version, which should be correct for all
built-in Django commands. User-supplied commands should
override this method.
"""
return django.get_version()
def usage(self, subcommand):
"""
Return a brief description of how to use this command, by
default from the attribute ``self.help``.
"""
usage = '%%prog %s [options] %s' % (subcommand, self.args)
if self.help:
return '%s\n\n%s' % (usage, self.help)
else:
return usage
def create_parser(self, prog_name, subcommand):
"""
Create and return the ``OptionParser`` which will be used to
parse the arguments to this command.
"""
return OptionParser(prog=prog_name,
usage=self.usage(subcommand),
version=self.get_version(),
option_list=self.option_list)
def print_help(self, prog_name, subcommand):
"""
Print the help message for this command, derived from
``self.usage()``.
"""
parser = self.create_parser(prog_name, subcommand)
parser.print_help()
def run_from_argv(self, argv):
"""
Set up any environment changes requested (e.g., Python path
and Django settings), then run this command.
"""
parser = self.create_parser(argv[0], argv[1])
options, args = parser.parse_args(argv[2:])
handle_default_options(options)
self.execute(*args, **options.__dict__)
def execute(self, *args, **options):
"""
Try to execute this command, performing model validation if
needed (as controlled by the attribute
``self.requires_model_validation``). If the command raises a
``CommandError``, intercept it and print it sensibly to
stderr.
"""
show_traceback = options.get('traceback', False)
# Switch to English, because django-admin.py creates database content
# like permissions, and those shouldn't contain any translations.
# But only do this if we can assume we have a working settings file,
# because django.utils.translation requires settings.
saved_lang = None
if self.can_import_settings:
try:
from django.utils import translation
saved_lang = translation.get_language()
translation.activate('en-us')
except ImportError, e:
# If settings should be available, but aren't,
# raise the error and quit.
if show_traceback:
traceback.print_exc()
else:
sys.stderr.write(smart_str(self.style.ERROR('Error: %s\n' % e)))
sys.exit(1)
try:
self.stdout = options.get('stdout', sys.stdout)
self.stderr = options.get('stderr', sys.stderr)
if self.requires_model_validation:
self.validate()
output = self.handle(*args, **options)
if output:
if self.output_transaction:
# This needs to be imported here, because it relies on
# settings.
from django.db import connections, DEFAULT_DB_ALIAS
connection = connections[options.get('database', DEFAULT_DB_ALIAS)]
if connection.ops.start_transaction_sql():
self.stdout.write(self.style.SQL_KEYWORD(connection.ops.start_transaction_sql()) + '\n')
self.stdout.write(output)
if self.output_transaction:
self.stdout.write('\n' + self.style.SQL_KEYWORD("COMMIT;") + '\n')
except CommandError, e:
if show_traceback:
traceback.print_exc()
else:
self.stderr.write(smart_str(self.style.ERROR('Error: %s\n' % e)))
sys.exit(1)
if saved_lang is not None:
translation.activate(saved_lang)
def validate(self, app=None, display_num_errors=False):
"""
Validates the given app, raising CommandError for any errors.
If app is None, then this will validate all installed apps.
"""
from django.core.management.validation import get_validation_errors
try:
from cStringIO import StringIO
except ImportError:
from StringIO import StringIO
s = StringIO()
num_errors = get_validation_errors(s, app)
if num_errors:
s.seek(0)
error_text = s.read()
raise CommandError("One or more models did not validate:\n%s" % error_text)
if display_num_errors:
self.stdout.write("%s error%s found\n" % (num_errors, num_errors != 1 and 's' or ''))
def handle(self, *args, **options):
"""
The actual logic of the command. Subclasses must implement
this method.
"""
raise NotImplementedError()