Flask之Blueprint

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Blueprint

Blueprint继承自_PackageBoundObject类

class Blueprint(_PackageBoundObject):    warn_on_modifications = False    _got_registered_once = False    def __init__(self, name, import_name, static_folder=None,                 static_url_path=None, template_folder=None,                 url_prefix=None, subdomain=None, url_defaults=None,                 root_path=None):        _PackageBoundObject.__init__(self, import_name, template_folder,                                     root_path=root_path)        self.name = name        self.url_prefix = url_prefix        self.subdomain = subdomain        self.static_folder = static_folder        self.static_url_path = static_url_path        self.deferred_functions = []        if url_defaults is None:            url_defaults = {}        self.url_values_defaults = url_defaults

除了Blueprint名称和导入的模块名，其他参数都有默认值，因此Blueprint可以这样初始化：

# -*- coding: utf-8 -*-from flask import Blueprintauth = Blueprint("auth", __name__)import views

Blueprint实例创建之后，需要调用Flask.register_blueprint()进行注册，我们来分析这个函数的处理流程：

    def register_blueprint(self, blueprint, **options):        """Registers a blueprint on the application.        .. versionadded:: 0.7        """        first_registration = False        if blueprint.name in self.blueprints:            assert self.blueprints[blueprint.name] is blueprint, \                'A blueprint\'s name collision occurred between %r and ' \                '%r.  Both share the same name "%s".  Blueprints that ' \                'are created on the fly need unique names.' % \                (blueprint, self.blueprints[blueprint.name], blueprint.name)        else:            self.blueprints[blueprint.name] = blueprint            self._blueprint_order.append(blueprint)            first_registration = True        blueprint.register(self, options, first_registration)

Flask有个列表blueprints，里面保存了所有Blueprint名，注册新的Blueprint时，首先以Blueprint为索引检查Flask列表blueprints，如果存在了，则给出告警；否则，将该Blueprint名称保存到列表blueprjints中，并调用Blueprint.register()进行深入注册。

继续分析Blueprint.register()处理流程：

    def register(self, app, options, first_registration=False):        """Called by :meth:`Flask.register_blueprint` to register a blueprint        on the application.  This can be overridden to customize the register        behavior.  Keyword arguments from        :func:`~flask.Flask.register_blueprint` are directly forwarded to this        method in the `options` dictionary.        """        self._got_registered_once = True        state = self.make_setup_state(app, options, first_registration)        if self.has_static_folder:            state.add_url_rule(self.static_url_path + '/<path:filename>',                               view_func=self.send_static_file,                               endpoint='static')        for deferred in self.deferred_functions:            deferred(state)

如果Blueprint有自己的static目录，则把static目录也添加到Flask路由规则中

BlueprintSetupState

这个类是Blueprint和Flask类之间的临时粘合剂。对象变量分别有Blueprint和Flask的引用、可选参数、url前缀等。需要注意的是，这里的可选参数是一般是调用Flask.register_blueprint()时传入的，优先级要高于Blueprint的可选参数

class BlueprintSetupState(object):    """Temporary holder object for registering a blueprint with the    application.  An instance of this class is created by the    :meth:`~flask.Blueprint.make_setup_state` method and later passed    to all register callback functions.    """    def __init__(self, blueprint, app, options, first_registration):        #: a reference to the current application        self.app = app        #: a reference to the blueprint that created this setup state.        self.blueprint = blueprint        #: a dictionary with all options that were passed to the        #: :meth:`~flask.Flask.register_blueprint` method.        self.options = options        self.first_registration = first_registration        subdomain = self.options.get('subdomain')        if subdomain is None:            subdomain = self.blueprint.subdomain        self.subdomain = subdomain        url_prefix = self.options.get('url_prefix')        if url_prefix is None:            url_prefix = self.blueprint.url_prefix        #: The prefix that should be used for all URLs defined on the        #: blueprint.        self.url_prefix = url_prefix        #: A dictionary with URL defaults that is added to each and every        #: URL that was defined with the blueprint.        self.url_defaults = dict(self.blueprint.url_values_defaults)        self.url_defaults.update(self.options.get('url_defaults', ()))    def add_url_rule(self, rule, endpoint=None, view_func=None, **options):        """A helper method to register a rule (and optionally a view function)        to the application.  The endpoint is automatically prefixed with the        blueprint's name.        """        if self.url_prefix:            rule = self.url_prefix + rule        options.setdefault('subdomain', self.subdomain)        if endpoint is None:            endpoint = _endpoint_from_view_func(view_func)        defaults = self.url_defaults        if 'defaults' in options:            defaults = dict(defaults, **options.pop('defaults'))        self.app.add_url_rule(rule, '%s.%s' % (self.blueprint.name, endpoint),                              view_func, defaults=defaults, **options)

初始化有几个地方需要注意（下面的可选参数都是调用Flask.register_blueprint()时传进来的）：

如果可选参数中存在"url_prefix"，则以可选参数为准，否则以Blueprint自带的"url_prefix"为准
如果可选参数中存在"subdomain"，则以可选参数为准，否则以Blueprint自带的"subdomain"为准

BlueprintSetupState唯一对外提供的方法是 def add_url_rule(self, rule, endpoint=None, view_func=None, **options)，该方法对url做些处理后，最终还是调用Flask的add_url_rule()来添加路由规则。这里我们之间查看Flask.add_url_rule()方法如何处理的：

class Flask(_PackageBoundObject):    @setupmethod    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

如果没有提供endpoint，则获取路由函数的名称作为路由规则的endpoint（这里说明，每个路由规则必然带有一个endpoint）
如果没有提供可选参数“methods”，则默认以GET方法来装饰，所有方法转换为大写
生成路由规则rule，并且添加到url_map中
如果路由规则处理函数不为空，则添加到view_functions字典中，key就是endpoint，value则是路由处理函数

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