def add_url_rule(self, rule, endpoint=None, view_func=None, **options):

        if endpoint is None:

            endpoint = _endpoint_from_view_func(view_func)

        options['endpoint'] = endpoint

        methods = options.pop('methods', None)

        # if the methods are not given and the view_func object knows its

        # methods we can use that instead.  If neither exists, we go with

        # a tuple of only ``GET`` as default.

        if methods is None:

            methods = getattr(view_func, 'methods', None) or ('GET',)

        if isinstance(methods, string_types):

            raise TypeError('Allowed methods have to be iterables of strings, '

                            'for example: @app.route(..., methods=["POST"])')

        methods = set(item.upper() for item in methods)

        # Methods that should always be added

        required_methods = set(getattr(view_func, 'required_methods', ()))

        # starting with Flask 0.8 the view_func object can disable and

        # force-enable the automatic options handling.

        provide_automatic_options = getattr(view_func,

            'provide_automatic_options', None)

        if provide_automatic_options is None:

            if 'OPTIONS' not in methods:

                provide_automatic_options = True

                required_methods.add('OPTIONS')

            else:

                provide_automatic_options = False

        # Add the required methods now.

        methods |= required_methods

        rule = self.url_rule_class(rule, methods=methods, **options)

        rule.provide_automatic_options = provide_automatic_options

        self.url_map.add(rule)

        if view_func is not None:

            old_func = self.view_functions.get(endpoint)

            if old_func is not None and old_func != view_func:

                raise AssertionError('View function mapping is overwriting an '

                                     'existing endpoint function: %s' % endpoint)

            self.view_functions[endpoint] = view_func

   def add_url_rule(self, rule, endpoint=None,  view_func=None, **options):

         if endpoint is None:

             # 如果没有提供endpoint参数，则默认用view_func的名字

             endpoint = _endpoint_from_view_func(view_func)

         # 把endpoint参数添加到options里面

         options['endpoint'] = endpoint

         # 从options中pop出methods参数，并把值赋给methods变量，如果没有则置为None

         methods = options.pop('methods', None)

         # moehods的值为None的情况下

         if methods is None:

             # 如果view_func函数中有这个methods参数，则使用view_func中的。如果没有则赋一个列表('GET',)给methods

             methods = getattr(view_func, 'methods', None) or ('GET',)

         # 如果methods是字符串类型

         if isinstance(methods, string_types):

             # 抛出一个异常：methods需要是一个可以迭代的字符串

             raise TypeError('Allowed methods have to be iterables of strings, '

                             'for example: @app.route(..., methods=["POST"])')

         # 把methods里面的item都改成大写

         methods = set(item.upper() for item in methods)

         # 在view_func里面定义了一个属性required_methods = ()

         # 作用：用来定义一些必须的方法，配合provide_automatic_options使用

         required_methods = set(getattr(view_func, 'required_methods', ()))

         # starting with Flask 0.8 the view_func object can disable and

         # force-enable the automatic options handling.

         # 在view_func里面定义了一个属性provide_automatic_options = None

         # 作用：用于禁用和强制启用一些自动选项

         provide_automatic_options = getattr(view_func,

             'provide_automatic_options', None)

         # 判断provide_automati_options是否为None

         if provide_automatic_options is None:

             # 如果OPTIONS字符串没有在methods里面

             if 'OPTIONS' not in methods:

                 # 则把provude_automatic_options改为True,并把OPTIONS添加到required_methods里面

                 provide_automatic_options = True

                 required_methods.add('OPTIONS')

             # 如果OPTIONS在methods里面，则把provide_automatic_options设置为False

             else:

                 provide_automatic_options = False

         # 合并required_methods和methods这两个集合到methods里面

         methods |= required_methods

         # 创建路由规则

         # 调用url_rule_class方法，由于在Flask类的全局变量中定义了：url_rule_class = Rule, Rule是werkzeug/routing.py里面的一个类

         # 也就是相当于实例化了Rule得到了rule对象，具体实例化后的结果请看Rule源码分析

         rule = self.url_rule_class(rule, methods=methods, **options)

         # 把provide_automatic_options属性添加到rule对象里面

         rule.provide_automatic_options = provide_automatic_options

         # 在Flask类的__init__里面定义了self.url_map = Map(),Map是werkzeug/routing.py里面的一个类

         # self.url_map相当与实例化了Map,.add则是调用了Map类里面的add方法

         # 具体运行结果，请参考Map源码分析，以及Map源码中的add方法分析

         self.url_map.add(rule)

         # 如果提供了view_func

         if view_func is not None:

             # 在flask类的__init__里面定义了self.view_functions = {},

             # 从字典里面取endpoint值并赋值为old_func，（endpoint是传递的参数，默认为视图函数名）

             old_func = self.view_functions.get(endpoint)

             # 如果old_func有值，并且不等于view_func

             if old_func is not None and old_func != view_func:

                 # 则抛出异常：视图函数映射被一个已经存在的函数名重写了

                 # 也就是说已经存在了一个endpoint:old_func的映射，但是old_fun却不是view_func，也就是说endpoint重复了

                 raise AssertionError('View function mapping is overwriting an '

                                      'existing endpoint function: %s' % endpoint)

             # 添加视图函数与endpoint映射到view_functions字典里面

             self.view_functions[endpoint] = view_func