__init__.py 文件源码

def fetch_command(self, subcommand):
        """
        Tries to fetch the given subcommand, printing a message with the
        appropriate command called from the command line (usually
        "django-admin" or "manage.py") if it can't be found.
        """
        # Get commands outside of try block to prevent swallowing exceptions
        commands = get_commands()
        try:
            app_name = commands[subcommand]
        except KeyError:
            if os.environ.get('DJANGO_SETTINGS_MODULE'):
                # If `subcommand` is missing due to misconfigured settings, the
                # following line will retrigger an ImproperlyConfigured exception
                # (get_commands() swallows the original one) so the user is
                # informed about it.
                settings.INSTALLED_APPS
            else:
                sys.stderr.write("No Django settings specified.\n")
            sys.stderr.write(
                "Unknown command: %r\nType '%s help' for usage.\n"
                % (subcommand, self.prog_name)
            )
            sys.exit(1)
        if isinstance(app_name, BaseCommand):
            # If the command is already loaded, use it directly.
            klass = app_name
        else:
            klass = load_command_class(app_name, subcommand)
        return klass