django從runserver到啓動成功

仿照django自帶的admin實現本身的admin組件
https://docs.djangoproject.com/zh-hans/2.2/ref/contrib/admin/

django從runserver到啓動成功

運行python manage.py runserver啓動
打開manage.py文件能夠發現該文件代碼很是簡單，主要乾了兩件事情:

1. 將settings.py文件的路徑存入系統環境變量os.environ。os.environ是一個繼承自抽象類_collections_abc.MutableMapping的os._Environ類的對象。
2. 將命令行參數sys.argv傳給execute_from_command_line執行。execute_from_command_line使用argv建立一個ManagementUtility對象，

def main():
    os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'Django_Admin.settings')
    try:
        from django.core.management import execute_from_command_line
    except ImportError as exc:
        raise ImportError(
            "Couldn't import Django. Are you sure it's installed and "
            "available on your PYTHONPATH environment variable? Did you "
            "forget to activate a virtual environment?"
        ) from exc
    execute_from_command_line(sys.argv)


if __name__ == '__main__':
    main()

execute_from_command_line

接着進入execute_from_command_line,execute_from_command_line使用argv建立一個ManagementUtility對象,而後調用其execute方法。

# django/core/management/__init__.py

def execute_from_command_line(argv=None):
    """Run a ManagementUtility."""
    utility = ManagementUtility(argv)
    utility.execute()

在這時,咱們發現因爲當前文件import了其餘依賴而初試化了apps對象和 settings對象.

因爲Import了django.apps.apps,apps對象會被初始化,這個對象主要負責存儲已安裝的django app的配置(AppConfig:包括app路徑,名稱,模塊,app_label,顯示名稱等)以及每一個app下的各個model.

# django/core/management/__init__.py

from django.apps import apps
from django.conf import settings

# django/apps/registry.py

apps = Apps(installed_apps=None)

因爲import 了django.conf.settings而初始化LazySettings類,它繼承自LazyObject類,LazyObject經過內嵌函數代理了__bytes__,__str__,__len__,__contains__,__iter__,__delitem__,__setitem__,__getitem__,__hash__,__ne__,__eq__,__class__,__dir__,__bool__方法,使這些方法在被調用以前檢查setting是否被加載,若是沒有的話,調用self._setup()安裝,而後再執行被調用的方法.也就是說全部繼承LazyObject的類,在調用上面方法時,會先調用_setup方法,只須要將初始化setting的代碼放到_setup裏,就能夠實現懶加載setting.

# django/conf/__init__.py
settings = LazySettings()

# django/utils/functional.py
def new_method_proxy(func):
    def inner(self, *args):
        if self._wrapped is empty:
            self._setup()
        return func(self._wrapped, *args)
    return inner

# django/utils/functional.py
class LazyObject:
    ...

    # Need to pretend to be the wrapped class, for the sake of objects that
    # care about this (especially in equality tests)
    __class__ = property(new_method_proxy(operator.attrgetter("__class__")))
    __eq__ = new_method_proxy(operator.eq)
    __lt__ = new_method_proxy(operator.lt)
    __gt__ = new_method_proxy(operator.gt)
    __ne__ = new_method_proxy(operator.ne)
    __hash__ = new_method_proxy(hash)

    # List/Tuple/Dictionary methods support
    __getitem__ = new_method_proxy(operator.getitem)
    __setitem__ = new_method_proxy(operator.setitem)
    __delitem__ = new_method_proxy(operator.delitem)
    __iter__ = new_method_proxy(iter)
    __len__ = new_method_proxy(len)
    __contains__ = new_method_proxy(operator.contains)
    
    ...

execute

繼續看ManagementUtility，它的execute方法主要完成了，命令行參數解析和運行command

• 命令行參數解析。首先生成一個繼承自ArgumentParser的CommandParser類，而後經過CommandParser類對參數進行解析。咱們在編寫django command時繼承的BaseCommand就是經過CommandParser來解析命令行參數的。
• 運行command。解析出subcommand，分別根據subcommand經過fetch_command函數獲得各類command對象，而command對象是經過獲取django\core\management\commands目錄和每一個app下management\commands下全部py文件中的Command類獲得。調用django.setup()對logging進行配置並調用apps.populate(settings.INSTALLED_APPS)配置安裝app。而後因爲Command類都繼承自BaseCommand,只須要調用run_from_argv方法便可對子命令行參數執行。

# django/core/management/__init__.py

    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.
        """
        try:
            subcommand = self.argv[1]
        except IndexError:
            subcommand = 'help'  # Display help if no arguments were given.

        # Preprocess options to extract --settings and --pythonpath.
        # These options could affect the commands that are available, so they
        # must be processed early.
        parser = CommandParser(usage='%(prog)s subcommand [options] [args]', add_help=False, allow_abbrev=False)
        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.

        try:
            settings.INSTALLED_APPS
        except ImproperlyConfigured as exc:
            self.settings_exception = exc
        except ImportError as exc:
            self.settings_exception = exc

        if settings.configured:
            # Start the auto-reloading dev server even if the code is broken.
            # The hardcoded condition is a code smell but we can't rely on a
            # flag on the command class because we haven't located it yet.
            if subcommand == 'runserver' and '--noreload' not in self.argv:
                try:
                    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)

            # In all other cases, django.setup() is required to succeed.
            else:
                django.setup()

        self.autocomplete()

        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:
                self.fetch_command(options.args[0]).print_help(self.prog_name, options.args[0])
        # Special-cases: We want 'django-admin --version' and
        # 'django-admin --help' to work, for backwards compatibility.
        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:
            self.fetch_command(subcommand).run_from_argv(self.argv)

autoreload.check_errors(django.setup)()其實也是調用django.setup方法

def setup(set_prefix=True):
    """
    Configure the settings (this happens as a side effect of accessing the
    first setting), configure logging and populate the app registry.
    Set the thread-local urlresolvers script prefix if `set_prefix` is True.
    """
    from django.apps import apps
    from django.conf import settings
    from django.urls import set_script_prefix
    from django.utils.log import configure_logging

    configure_logging(settings.LOGGING_CONFIG, settings.LOGGING)
    if set_prefix:
        set_script_prefix(
            '/' if settings.FORCE_SCRIPT_NAME is None else settings.FORCE_SCRIPT_NAME
        )
    apps.populate(settings.INSTALLED_APPS)

apps.populate(settings.INSTALLED_APPS)

apps.populate(settings.INSTALLED_APPS)將會根據settings.INSTALLED_APPS中的配置查找app,以後分別調用每一個app_config的ready方法。因爲apps.populate是加了鎖防止重複執行的，因此每一個app的app_config.ready只會初始化一次，咱們若是有須要在django啓動時執行一次的操做，能夠將其放入app_config.ready中。

在調用app_config.ready以前，會先將全部的models加載進來。其經過MODELS_MODULE_NAME="models"; import_module(app_name,MODELS_MODULE_NAME)的方式導入models。

def populate(self, installed_apps=None):
        """
        Load application configurations and models.

        Import each application module and then each model module.

        It is thread-safe and idempotent, but not reentrant.
        """
        if self.ready:
            return

        # populate() might be called by two threads in parallel on servers
        # that create threads before initializing the WSGI callable.
        with self._lock:
            if self.ready:
                return

            # An RLock prevents other threads from entering this section. The
            # compare and set operation below is atomic.
            if self.loading:
                # Prevent reentrant calls to avoid running AppConfig.ready()
                # methods twice.
                raise RuntimeError("populate() isn't reentrant")
            self.loading = True

            # Phase 1: initialize app configs and import app modules.
            for entry in installed_apps:
                if isinstance(entry, AppConfig):
                    app_config = entry
                else:
                    app_config = AppConfig.create(entry)
                if app_config.label in self.app_configs:
                    raise ImproperlyConfigured(
                        "Application labels aren't unique, "
                        "duplicates: %s" % app_config.label)

                self.app_configs[app_config.label] = app_config
                app_config.apps = self

            # Check for duplicate app names.
            counts = Counter(
                app_config.name for app_config in self.app_configs.values())
            duplicates = [
                name for name, count in counts.most_common() if count > 1]
            if duplicates:
                raise ImproperlyConfigured(
                    "Application names aren't unique, "
                    "duplicates: %s" % ", ".join(duplicates))

            self.apps_ready = True

            # Phase 2: import models modules.
            for app_config in self.app_configs.values():
                app_config.import_models()

            self.clear_cache()

            self.models_ready = True

            # Phase 3: run ready() methods of app configs.
            for app_config in self.get_app_configs():
                app_config.ready()

            self.ready = True
            self.ready_event.set()

def import_models(self):
        # Dictionary of models for this app, primarily maintained in the
        # 'all_models' attribute of the Apps this AppConfig is attached to.
        self.models = self.apps.all_models[self.label]

        if module_has_submodule(self.module, MODELS_MODULE_NAME):
            models_module_name = '%s.%s' % (self.name, MODELS_MODULE_NAME)
            self.models_module = import_module(models_module_name)

AdminConfig

看一下admin的AdminConfig

class SimpleAdminConfig(AppConfig):
    """Simple AppConfig which does not do automatic discovery."""

    default_site = 'django.contrib.admin.sites.AdminSite'
    name = 'django.contrib.admin'
    verbose_name = _("Administration")

    def ready(self):
        checks.register(check_dependencies, checks.Tags.admin)
        checks.register(check_admin_app, checks.Tags.admin)


class AdminConfig(SimpleAdminConfig):
    """The default AppConfig for admin which does autodiscovery."""

    def ready(self):
        super().ready()
        self.module.autodiscover()

自動掃描每一個app下的admin包, 將裏面的東西註冊到site = DefaultAdminSite()中
site是一個單例對象

def autodiscover():
    autodiscover_modules('admin', register_to=site)

autodiscover_modules函數自動加載每一個app下的admin.py文件

def autodiscover_modules(*args, **kwargs):
    """
    Auto-discover INSTALLED_APPS modules and fail silently when
    not present. This forces an import on them to register any admin bits they
    may want.

    You may provide a register_to keyword parameter as a way to access a
    registry. This register_to object must have a _registry instance variable
    to access it.
    """
    from django.apps import apps

    register_to = kwargs.get('register_to')
    for app_config in apps.get_app_configs():
        for module_to_search in args:
            # Attempt to import the app's module.
            try:
                if register_to:
                    before_import_registry = copy.copy(register_to._registry)

                import_module('%s.%s' % (app_config.name, module_to_search))
            except Exception:
                # Reset the registry to the state before the last import
                # as this import will have to reoccur on the next request and
                # this could raise NotRegistered and AlreadyRegistered
                # exceptions (see #8245).
                if register_to:
                    register_to._registry = before_import_registry

                # Decide whether to bubble up this error. If the app just
                # doesn't have the module in question, we can ignore the error
                # attempting to import it, otherwise we want it to bubble up.
                if module_has_submodule(app_config.module, module_to_search):
                    raise

admin.site.register()

def register(self, model_or_iterable, admin_class=None, **options):
        """
        Register the given model(s) with the given admin class.

        The model(s) should be Model classes, not instances.

        If an admin class isn't given, use ModelAdmin (the default admin
        options). If keyword arguments are given -- e.g., list_display --
        apply them as options to the admin class.

        If a model is already registered, raise AlreadyRegistered.

        If a model is abstract, raise ImproperlyConfigured.
        """
        admin_class = admin_class or ModelAdmin
        if isinstance(model_or_iterable, ModelBase):
            model_or_iterable = [model_or_iterable]
        for model in model_or_iterable:
            if model._meta.abstract:
                raise ImproperlyConfigured(
                    'The model %s is abstract, so it cannot be registered with admin.' % model.__name__
                )

            if model in self._registry:
                raise AlreadyRegistered('The model %s is already registered' % model.__name__)

            # Ignore the registration if the model has been
            # swapped out.
            if not model._meta.swapped:
                # If we got **options then dynamically construct a subclass of
                # admin_class with those **options.
                if options:
                    # For reasons I don't quite understand, without a __module__
                    # the created class appears to "live" in the wrong place,
                    # which causes issues later on.
                    options['__module__'] = __name__
                    admin_class = type("%sAdmin" % model.__name__, (admin_class,), options)

                # Instantiate the admin class to save in the registry
                self._registry[model] = admin_class(model, self)

print(admin.site._registry)

{<class 'django.contrib.auth.models.Group'>: <django.contrib.auth.admin.GroupAdmin object at 0x0000019BA62B9BE0>, 
<class 'django.contrib.auth.models.User'>: <django.contrib.auth.admin.UserAdmin object at 0x0000019BA62E9BA8>, 
<class 'book.models.Book'>: <django.contrib.admin.options.ModelAdmin object at 0x0000019BA62E9DD8>, 
<class 'book.models.Author'>: <django.contrib.admin.options.ModelAdmin object at 0x0000019BA62FDC50>}

回到execute函數中

self.fetch_command(subcommand).run_from_argv(self.argv)爲重點,是用戶輸入的命令的真實入口

def fetch_command(self, subcommand):
        """
        Try 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")
            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)
        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 load_command_class(app_name, name):
    """
    Given a command name and an application name, return the Command
    class instance. Allow all errors raised by the import process
    (ImportError, AttributeError) to propagate.
    """
    module = import_module('%s.management.commands.%s' % (app_name, name))
    return module.Command()

其中fetch_command根據subcommand返回對應的命令處理文件,load_command_class函數返回module.Command(),在本例中就是self.fetch_command(subcommand)就是runserver.Command()

命令處理文件放在django/core/management/commands下面
打開django/core/management/commands/runserver.py文件
Command類繼承了BaseCommand類, 查看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

execute函數返回的是handle函數

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['force_color'] and options['no_color']:
            raise CommandError("The --no-color and --force-color options can't be used together.")
        if options['force_color']:
            self.style = color_style(force_color=True)
        elif 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

查看Command類的handle函數, Command重寫了父類的handle方法

def handle(self, *args, **options):
        if not settings.DEBUG and not settings.ALLOWED_HOSTS:
            raise CommandError('You must set settings.ALLOWED_HOSTS if DEBUG is False.')

        self.use_ipv6 = options['use_ipv6']
        if self.use_ipv6 and not socket.has_ipv6:
            raise CommandError('Your Python does not support IPv6.')
        self._raw_ipv6 = False
        if not options['addrport']:
            self.addr = ''
            self.port = self.default_port
        else:
            m = re.match(naiveip_re, options['addrport'])
            if m is None:
                raise CommandError('"%s" is not a valid port number '
                                   'or address:port pair.' % options['addrport'])
            self.addr, _ipv4, _ipv6, _fqdn, self.port = m.groups()
            if not self.port.isdigit():
                raise CommandError("%r is not a valid port number." % self.port)
            if self.addr:
                if _ipv6:
                    self.addr = self.addr[1:-1]
                    self.use_ipv6 = True
                    self._raw_ipv6 = True
                elif self.use_ipv6 and not _fqdn:
                    raise CommandError('"%s" is not a valid IPv6 address.' % self.addr)
        if not self.addr:
            self.addr = self.default_addr_ipv6 if self.use_ipv6 else self.default_addr
            self._raw_ipv6 = self.use_ipv6
        self.run(**options)

    def run(self, **options):
        """Run the server, using the autoreloader if needed."""
        use_reloader = options['use_reloader']

        if use_reloader:
            autoreload.run_with_reloader(self.inner_run, **options)
        else:
            self.inner_run(None, **options)

    def inner_run(self, *args, **options):
        # If an exception was silenced in ManagementUtility.execute in order
        # to be raised in the child process, raise it now.
        autoreload.raise_last_exception()

        threading = options['use_threading']
        # 'shutdown_message' is a stealth option.
        shutdown_message = options.get('shutdown_message', '')
        quit_command = 'CTRL-BREAK' if sys.platform == 'win32' else 'CONTROL-C'

        self.stdout.write("Performing system checks...\n\n")
        self.check(display_num_errors=True)
        # Need to check migrations here, so can't use the
        # requires_migrations_check attribute.
        self.check_migrations()
        now = datetime.now().strftime('%B %d, %Y - %X')
        self.stdout.write(now)
        self.stdout.write((
            "Django version %(version)s, using settings %(settings)r\n"
            "Starting development server at %(protocol)s://%(addr)s:%(port)s/\n"
            "Quit the server with %(quit_command)s.\n"
        ) % {
            "version": self.get_version(),
            "settings": settings.SETTINGS_MODULE,
            "protocol": self.protocol,
            "addr": '[%s]' % self.addr if self._raw_ipv6 else self.addr,
            "port": self.port,
            "quit_command": quit_command,
        })

        try:
            handler = self.get_handler(*args, **options)
            run(self.addr, int(self.port), handler,
                ipv6=self.use_ipv6, threading=threading, server_cls=self.server_cls)
        except socket.error as e:
            # Use helpful error messages instead of ugly tracebacks.
            ERRORS = {
                errno.EACCES: "You don't have permission to access that port.",
                errno.EADDRINUSE: "That port is already in use.",
                errno.EADDRNOTAVAIL: "That IP address can't be assigned to.",
            }
            try:
                error_text = ERRORS[e.errno]
            except KeyError:
                error_text = e
            self.stderr.write("Error: %s" % error_text)
            # Need to use an OS exit because sys.exit doesn't work in a thread
            os._exit(1)
        except KeyboardInterrupt:
            if shutdown_message:
                self.stdout.write(shutdown_message)
            sys.exit(0)

最終經過WSGIServer類啓動線程來處理http請求

def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
    server_address = (addr, port)
    if threading:
        httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {})
    else:
        httpd_cls = server_cls
    httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)
    if threading:
        # ThreadingMixIn.daemon_threads indicates how threads will behave on an
        # abrupt shutdown; like quitting the server by the user or restarting
        # by the auto-reloader. True means the server will not wait for thread
        # termination before it quits. This will make auto-reloader faster
        # and will prevent the need to kill the server manually if a thread
        # isn't terminating correctly.
        httpd.daemon_threads = True
    httpd.set_app(wsgi_handler)
    httpd.serve_forever()

啓動流程

runserver方式以command的方式啓動wsgi. 先初始化apps和settings對象;接着得到全部command對象;懶加載調用setting._setup()方法安裝配置;接着解析獲得子命令,調用django.setup()配置logging和初始化app_config,導入models;根據子命令獲取command對象並將參數傳遞給其並執行,其餘參數根據management\commands中的command文件的定義進行解析,而後調用handle方法進行執行;而後調用run方法啓動wsgi.

參考:
http://www.javashuo.com/article/p-dmxvfetu-bp.html