Flask快速入门(3) — flask路由的本质

目录

from flask import Flask
app = Flask(__name__)

@app.route('/')
def index():
    return 'ok'

if __name__ == '__main__':
    app.run()

从这个简单的代码入口,来剖析一下路由@app.route('/')

route():就是一个加在index()上的装饰器

def route(self, rule, **options):  # rule:匹配规则,options参数字典
    def decorator(f):  
        endpoint = options.pop("endpoint", None)  # 如果option中有endpoint就取出,否则endpoint=None
        self.add_url_rule(rule, endpoint, f, **options)  # f就是装饰器装饰的视图函数 index
        return f
    return decorator

获取的信息:

(1)route传参时可以指定 endpoint = '别名',endpoint是给这个路由取的别名,用作反向解析,稍后再会介绍。没有传时为None。

(2)主要是执行了add_url_rule方法将匹配规定与视图函数的对应关系添加到路由中

add_url_rule():将匹配规定与视图函数的对应关系添加到路由

@setupmethod
def add_url_rule(self,rule,endpoint=None,view_func=None,provide_automatic_options=None,**options):
    # 其中rule是必须要传入的,endpoint是别名,view_func是函数名
    if endpoint is None:
        endpoint = _endpoint_from_view_func(view_func)  # 如果没有别名就执行该函数,并且将视图函数当做参数传入了,稍后再看
    options["endpoint"] = endpoint
    methods = options.pop("methods", None)  # 如果options中有methods则取出,否则为methods = None
    
    # 如果methods为None的话,默认为view_func中的methods属性值,或者为('GET',)请求
    if methods is None:
        methods = getattr(view_func, "methods", None) or ("GET",)
    # 如果methods是字符串类型,string_types=>(str, unicode),则抛出异常
    if isinstance(methods, string_types):
        raise TypeError(
            "Allowed methods have to be iterables of strings, "
            'for example: @app.route(..., methods=["POST"])'
        )
    # 循环遍历methods,并转成大写、去重
    methods = set(item.upper() for item in methods)

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

    if provide_automatic_options is None:
        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

    methods |= required_methods

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

    self.url_map.add(rule)  # 添加匹配规则
    if view_func is not None:
        old_func = self.view_functions.get(endpoint)  # 默认self.view_functions={},所以old_func=None
        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  # 将 endpoint 与 view_func 对应。{endpoint:view_func}

一眼看到上面的源码是不是懵,在代码中相关的部分添加了注释。获取的信息:

(1)methods是定义该视图函数的请求方式,如果没有指定就默认为get方式

(2)methods传参是不能传字符串类型,应该设置:methods=('post',),参数不区分大小写,即'post'与‘POST’都可以传入

(3)将endpoint的值与函数名对应,比如endpoint='xxx':则相当于是给视图函数index取了一个别名。如果没有endpoint,执行_endpoint_from_view_func(view_func),endpoint=函数名

def _endpoint_from_view_func(view_func):
    """Internal helper that returns the default endpoint for a given
    function.  This always is the function name.
    """
    assert view_func is not None, "expected view func if endpoint is not provided."
    return view_func.__name__  # 返回的就是函数名

总结:

(1)路由本质上就是执行了add_url_rule函数,所以也可以通过该函数来添加路由app.add_url_rule('/',endpoint='xxx',view_func=index)

(2)endpoint:用来指定别名,没有指定就用函数名字

(3)methods:用来指定视图函数的请求方式,没有指定就默认为get方法

(4)url_for:通过别名来做反向路由解析

from flask import Flask, request,redirect,url_for
app = Flask(__name__)
app.debug =True

# @app.route('/')
def index():
    return 'dasdk'
app.add_url_rule('/',endpoint='xxx',view_func=index)  # 用来绑定路由

@app.route('/login')
def login():
    url = url_for('xxx')  # 反向路由解析,url此时指向index视图函数
    return redirect(url)

if __name__ == '__main__':
    app.run()
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