Django源码之命令解析

环境：python3.6.8  django2.1.3

django命令源码简介

通过django-admin命令可获取django自带的24个命令，具体命令如下：

[django]
    check
    compilemessages
    createcachetable
    dbshell
    diffsettings
    dumpdata
    flush
    inspectdb
    loaddata
    makemessages
    makemigrations
    migrate
    runserver
    sendtestemail
    shell
    showmigrations
    sqlflush
    sqlmigrate
    sqlsequencereset
    squashmigrations
    startapp
    startproject
    test
    testserver

以上命令都是由django默认提供支持的命令，并且这些命令对应的具体执行文件都是位于django/core/management/commands/文件中，并且都是通过django/bin/django-admin.py文件执行来调用，由此先看下django-admin的具体代码分析:

#!/usr/bin/env python
from django.core import management

if __name__ == "__main__":
    management.execute_from_command_line()

通过以上代码可见，调用management包的__init__.py文件中的execute_from_command_line函数:

def execute_from_command_line(argv=None):
    """Run a ManagementUtility."""
    utility = ManagementUtility(argv)  # 实例化一个对象，通过命令行传参数，执行指定命令
    utility.execute()

实例化对象类，并执行命令行：

class ManagementUtility:
    """
    Encapsulate the logic of the django-admin and manage.py utilities.
    """
    def __init__(self, argv=None):
        self.argv = argv or sys.argv[:]
        self.prog_name = os.path.basename(self.argv[0])
        if self.prog_name == '__main__.py':
            self.prog_name = 'python -m django'
        self.settings_exception = None

    def main_help_text(self, commands_only=False):
        """Return the script's main help text, as a string."""
        if commands_only:
            usage = sorted(get_commands())
        else:
            usage = [
                "",
                "Type '%s help ' for help on a specific subcommand." % self.prog_name,
                "",
                "Available subcommands:",
            ]
            commands_dict = defaultdict(lambda: [])
            for name, app in get_commands().items():
                if app == 'django.core':
                    app = 'django'
                else:
                    app = app.rpartition('.')[-1]
                commands_dict[app].append(name)
            style = color_style()
            for app in sorted(commands_dict):
                usage.append("")
                usage.append(style.NOTICE("[%s]" % app))
                for name in sorted(commands_dict[app]):
                    usage.append("    %s" % name)
            # Output an extra note if settings are not properly configured
            if self.settings_exception is not None:
                usage.append(style.NOTICE(
                    "Note that only Django core commands are listed "
                    "as settings are not properly configured (error: %s)."
                    % self.settings_exception))

        return '\n'.join(usage)

    def fetch_command(self, subcommand):
        """
        执行指定命令行
        """
        # Get commands outside of try block to prevent swallowing exceptions
        # 获取django的所有命令行字典，以及项目自定义命令
        commands = get_commands()
        # 根据用户命令参数获取指定的命令操作应用对象或路径
        try:
            app_name = commands[subcommand]
        except KeyError:
            if os.environ.get('DJANGO_SETTINGS_MODULE'):
                settings.INSTALLED_APPS
            else:
                sys.stderr.write("No Django settings specified.\n")
            possible_matches = get_close_matches(subcommand, commands)
            sys.stderr.write('Unknown command: %r' % subcommand)
            if possible_matches:
                sys.stderr.write('. Did you mean %s?' % possible_matches[0])
            sys.stderr.write("\nType '%s help' for usage.\n" % self.prog_name)
            sys.exit(1)

        # 判断获取的时对命令对象还是路径，如果时路径则获取其对应的实例对象
        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

    def autocomplete(self):
        """
        Output completion suggestions for BASH.

        The output of this function is passed to BASH's `COMREPLY` variable and
        treated as completion suggestions. `COMREPLY` expects a space
        separated string as the result.

        The `COMP_WORDS` and `COMP_CWORD` BASH environment variables are used
        to get information about the cli input. Please refer to the BASH
        man-page for more information about this variables.

        Subcommand options are saved as pairs. A pair consists of
        the long option string (e.g. '--exclude') and a boolean
        value indicating if the option requires arguments. When printing to
        stdout, an equal sign is appended to options which require arguments.

        Note: If debugging this function, it is recommended to write the debug
        output in a separate file. Otherwise the debug output will be treated
        and formatted as potential completion suggestions.
        """
        # Don't complete if user hasn't sourced bash_completion file.
        if 'DJANGO_AUTO_COMPLETE' not in os.environ:
            return

        cwords = os.environ['COMP_WORDS'].split()[1:]
        cword = int(os.environ['COMP_CWORD'])

        try:
            curr = cwords[cword - 1]
        except IndexError:
            curr = ''

        subcommands = list(get_commands()) + ['help']
        options = [('--help', False)]

        # subcommand
        if cword == 1:
            print(' '.join(sorted(filter(lambda x: x.startswith(curr), subcommands))))
        # subcommand options
        # special case: the 'help' subcommand has no options
        elif cwords[0] in subcommands and cwords[0] != 'help':
            subcommand_cls = self.fetch_command(cwords[0])
            # special case: add the names of installed apps to options
            if cwords[0] in ('dumpdata', 'sqlmigrate', 'sqlsequencereset', 'test'):
                try:
                    app_configs = apps.get_app_configs()
                    # Get the last part of the dotted path as the app name.
                    options.extend((app_config.label, 0) for app_config in app_configs)
                except ImportError:
                    # Fail silently if DJANGO_SETTINGS_MODULE isn't set. The
                    # user will find out once they execute the command.
                    pass
            parser = subcommand_cls.create_parser('', cwords[0])
            options.extend(
                (min(s_opt.option_strings), s_opt.nargs != 0)
                for s_opt in parser._actions if s_opt.option_strings
            )
            # filter out previously specified options from available options
            prev_opts = {x.split('=')[0] for x in cwords[1:cword - 1]}
            options = (opt for opt in options if opt[0] not in prev_opts)

            # filter options by current input
            options = sorted((k, v) for k, v in options if k.startswith(curr))
            for opt_label, require_arg in options:
                # append '=' to options which require args
                if require_arg:
                    opt_label += '='
                print(opt_label)
        # Exit code of the bash completion function is never passed back to
        # the user, so it's safe to always exit with 0.
        # For more details see #25420.
        sys.exit(0)

    def execute(self):
        """
        Given the command-line arguments, figure out which subcommand is being
        run, create a parser appropriate to that command, and run it.
        """
        # 获取命令行第一个参数，如果没有则默认执行help命令
        try:
            subcommand = self.argv[1]
        except IndexError:
            subcommand = 'help'  # Display help if no arguments were given.

        
        # 增加命令说明
        parser = CommandParser(usage='%(prog)s subcommand [options] [args]', add_help=False, allow_abbrev=False)
        # 解析命令行中指定settings和pythonpath的文件路径，没有则使用默认
        parser.add_argument('--settings')
        parser.add_argument('--pythonpath')
        parser.add_argument('args', nargs='*')  # catch-all
        try:
            options, args = parser.parse_known_args(self.argv[2:])
            handle_default_options(options)
        except CommandError:
            pass  # Ignore any option errors at this point.

        # 判断配置中已经导入的apps，如果导入不存在的app则会报错
        try:
            settings.INSTALLED_APPS
        except ImproperlyConfigured as exc:
            self.settings_exception = exc
        except ImportError as exc:
            self.settings_exception = exc

        if settings.configured:

            # 验证是否使用runserver命令并不关闭自动重启服务
            if subcommand == 'runserver' and '--noreload' not in self.argv:
                try:
                    # 调用自动检测文件是否修改如果修改则自动重新启动Django服务
                    autoreload.check_errors(django.setup)()
                except Exception:
                    # The exception will be raised later in the child process
                    # started by the autoreloader. Pretend it didn't happen by
                    # loading an empty list of applications.
                    apps.all_models = defaultdict(OrderedDict)
                    apps.app_configs = OrderedDict()
                    apps.apps_ready = apps.models_ready = apps.ready = True

                    # Remove options not compatible with the built-in runserver
                    # (e.g. options for the contrib.staticfiles' runserver).
                    # Changes here require manually testing as described in
                    # #27522.
                    _parser = self.fetch_command('runserver').create_parser('django', 'runserver')
                    _options, _args = _parser.parse_known_args(self.argv[2:])
                    for _arg in _args:
                        self.argv.remove(_arg)

            else:
                # 启动Django项目，不进行自动重启服务
                django.setup()

        self.autocomplete()

        # 处理help命令，打印django支持所有命令
        if subcommand == 'help':
            if '--commands' in args:
                sys.stdout.write(self.main_help_text(commands_only=True) + '\n')
            elif not options.args:
                sys.stdout.write(self.main_help_text() + '\n')
            else:
                # 对应命令帮助说明
                self.fetch_command(options.args[0]).print_help(self.prog_name, options.args[0])
        # 查询django版本以及指定命令的使用说明
        elif subcommand == 'version' or self.argv[1:] == ['--version']:
            sys.stdout.write(django.get_version() + '\n')
        elif self.argv[1:] in (['--help'], ['-h']):
            sys.stdout.write(self.main_help_text() + '\n')
        else:
            # 如果命令行输入单个命令，则寻找该命令，然后执行输入的参数
            self.fetch_command(subcommand).run_from_argv(self.argv)

当使用命令行工具创建django项目和应用，此时使用的命令为startproject,startapp,这两个命令比较相似，实现的功能都是讲django/conf目录下的project_template和app_template两个模板进行一定数据的渲染后生成一个完整的项目到指定目录下。 
而执行的参数为django-admin startapp testapp，此时就会执行到 以上源码的

def fetch_command(self, subcommand)方法获取命令的实例执行其父类BaseCommand的run_from_argv方法：

    def run_from_argv(self, argv):
        """
        Set up any environment changes requested (e.g., Python path
        and Django settings), then run this command. If the
        command raises a ``CommandError``, intercept it and print it sensibly
        to stderr. If the ``--traceback`` option is present or the raised
        ``Exception`` is not ``CommandError``, raise it.
        """
        self._called_from_command_line = True
        parser = self.create_parser(argv[0], argv[1])

        options = parser.parse_args(argv[2:])
        cmd_options = vars(options)
        # Move positional args out of options to mimic legacy optparse
        args = cmd_options.pop('args', ())
        handle_default_options(options)
        try:
            self.execute(*args, **cmd_options)
        except Exception as e:
            if options.traceback or not isinstance(e, CommandError):
                raise

            # SystemCheckError takes care of its own formatting.
            if isinstance(e, SystemCheckError):
                self.stderr.write(str(e), lambda x: x)
            else:
                self.stderr.write('%s: %s' % (e.__class__.__name__, e))
            sys.exit(1)
        finally:
            try:
                connections.close_all()
            except ImproperlyConfigured:
                # Ignore if connections aren't setup at this point (e.g. no
                # configured settings).
                pass



    def execute(self, *args, **options):
        """
        Try to execute this command, performing system checks if needed (as
        controlled by the ``requires_system_checks`` attribute, except if
        force-skipped).
        """
        if options['no_color']:
            self.style = no_style()
            self.stderr.style_func = None
        if options.get('stdout'):
            self.stdout = OutputWrapper(options['stdout'])
        if options.get('stderr'):
            self.stderr = OutputWrapper(options['stderr'], self.stderr.style_func)

        if self.requires_system_checks and not options.get('skip_checks'):
            self.check()
        if self.requires_migrations_checks:
            self.check_migrations()
        output = self.handle(*args, **options)
        if output:
            if self.output_transaction:
                connection = connections[options.get('database', DEFAULT_DB_ALIAS)]
                output = '%s\n%s\n%s' % (
                    self.style.SQL_KEYWORD(connection.ops.start_transaction_sql()),
                    output,
                    self.style.SQL_KEYWORD(connection.ops.end_transaction_sql()),
                )
            self.stdout.write(output)
        return output

run_from_argv调用execute方法，然后继续调用handler方法。至此，startapp和startproject命令的解析已经完成，此时就可以完成项目和应用的创建。其他命令类似以上执行过程，其中针对项目中自定义命令在进行get_commands()中进行收集：

def get_commands():
    """
    获取django核心命令和项目应用中自定义命令
    """
    commands = {name: 'django.core' for name in find_commands(__path__[0])}

    if not settings.configured:
        return commands

    # 获取项目中app，并获取其指定management中自定义命令，命令名称通常为文件名
    for app_config in reversed(list(apps.get_app_configs())):
        path = os.path.join(app_config.path, 'management')
        commands.update({name: app_config.name for name in find_commands(path)})

    return commands

动态执行过程如下图：