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Flask简介

点滴 admin 4年前 (2015-10-31) 226次浏览 已收录 扫描二维码

Flask是一个相对于Django而言轻量级的Web框架。

和Django大包大揽不同,Flask建立于一系列的开源软件包之上,这其中
最主要的是WSGI应用开发库Werkzeug和模板引擎Jinja

Flask简介 Flask简介

策略 :werkzeug和Jinja这两个库和Flask一样,都是pocoo团队开发的。这
或许体现了pocoo与Django竞争时关于生态的一种策略,这种策略的自然
延伸是Flask框架中没有包含数据库方面的构件,无论ORM还是其他。

关注点 :Flask是一个WSGI应用框架,这意味着我们进行Flask开发时,不需要
关注网络方面的操作,Flask应用的入口是封装过的网络请求包,出口是
网络响应,我们仅需要关注这个阶段内的处理逻辑。

WSGI服务器 :Flask虽然内置了简单的WSGI服务器,但其性能仅仅适用于开发期的调试。
Flask官网推荐了多种WSGI服务器,实现方式从多进程到多线程到协程,
这方面的选择我们在本课程中将不涉及。

REST适应性 :虽然Flask和Django一样,最初的出发点都是服务端的动态网页应用。但
Flask的设计使之也相当适用于面向资源的REST架构,在越来越移动化
并且单页应用越来越重要的WEB开发领域,这是Flask相对于Django相当
大的优势。

Hello Flask

编写一个基于Flask的hello world相当容易:

1、导入Flask类

    <ol class="linenums">
        
        <li class="L0">
            <span class="kwd">from</span><span class="pln"> <a href="https://www.whatled.com/post-tag/flask" title="查看更多关于flask的文章" target="_blank">flask</a> </span><span class="kwd">import</span><span class="pln"> </span><span class="typ">Flask</span>
        </li>

    </ol>

Flask类是Flask框架的核心类,它实现了WSGI应用规范。

2、创建Flask实例

    <ol class="linenums">
        
        <li class="L0">
            <span class="pln">app </span><span class="pun">=</span><span class="pln"> </span><span class="typ">Flask</span><span class="pun">(</span><span class="pln">__name__</span><span class="pun">)</span>
        </li>

    </ol>

Flask构造函数的第一个参数指定一个引入名/import_name。Flask框架
使用这个名字进行静态资源、模板、错误信息的定位。除非你清楚的理解它的
作用,通常情况下,我们总应该使用特殊变量__name__

Flask实例是可调用的(具有__call__方法),这个实例可以直接对接
WSGI服务器。

3、注册路由

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@route</span><span class="pun">(</span><span class="str">’/’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> index</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’Hello,Flask!’</span>
        </li>

    </ol>

注册路由就是建立URL规则和处理函数之间的关联。Flask框架依赖于路由 完成HTTP请求的分发。

路由中的函数被称为视图函数,其返回值将作为HTTP响应的正文内容。

4、对接并启动WSGI服务器

Flask封装了一个简单的开发用WSGI服务器,我们可以通过调用run() 启动服务器运行:

    <ol class="linenums">
        
        <li class="L0">
            <span class="pln">app</span><span class="pun">.</span><span class="pln">run</span><span class="pun">(</span><span class="pln">host</span><span class="pun">=</span><span class="str">’0.0.0.0’</span><span class="pun">,</span><span class="pln">port</span><span class="pun">=</span><span class="lit">80</span><span class="pun">)</span>
        </li>

    </ol>
1. 点击[运行]按钮,运行示例程序。
2. 点击[测试]按钮,在新开启的浏览器页面内查看访问结果

概述

路由是MVC架构的Web框架中相当重要的一个概念,也是本节课程的重点。

顾名思意,路由就是在迷茫中找出一条路的意思。在Flask框架中,路由
就表示为用户请求的URL找出其对应的处理函数之意。

Flask简介

在本节课程,我们将主要从以下几个方面讲解Flask框架中的路由:

  • 如何为应用注册路由?
  • 如何为路由指定其支持的HTTP方法?
  • 如何匹配动态URL?
  • 如何对URL中的变量类型进行过滤?
  • 如何理解访问点/endpoint?
  • 如何为应用设定静态路由?
  • 如何避免硬编码指向其他视图的URL?

现在开始吧。

注册路由

在Flask应用中,路由是指用户请求的URL视图函数之间的映射。Flask框架
根据HTTP请求的URL在路由表中匹配预定义的URL规则,找到对应的视图函数,
并将视图函数的执行结果返回WSGI服务器:

Flask简介

可见路由表在Flask应用中处于相当核心的位置。路由表的内容是由应用开发者填充。

route装饰器 :可以使用Flask应用实例的route装饰器将一个URL规则绑定到
一个视图函数上。

例如,下面的示例将URL规则/test绑定到视图函数test()上:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/test’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> test</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’this is response’</span>
        </li>

    </ol>

如果这个应用部署在主机ezhost.com的根目录下,那么当用户访问:

    <ol class="linenums">
        
        <li class="L0">
            <span class="pln">http</span><span class="pun">:</span><span class="com">//ezhost.com/test</span>
        </li>

    </ol>

Flask框架就会调用我们的test()函数,其返回结果就传递给WSGI服务器发送给访问者。

add_url_rule() :另一种等价的写法是使用Flask应用实例的add_url_route()方法。
下面的示例注册了一个与前例相同的路由:

    <ol class="linenums">
        
        <li class="L0">
            <span class="kwd">def</span><span class="pln"> test</span><span class="pun">():</span>
        </li>

        <li class="L1">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’this is response’</span>
        </li>

        <li class="L2">
            <span class="pln">app</span><span class="pun">.</span><span class="pln">add_url_route</span><span class="pun">(</span><span class="str">’/test’</span><span class="pun">,</span><span class="pln">view_func</span><span class="pun">=</span><span class="pln">test</span><span class="pun">)</span>
        </li>

    </ol>

其实,route装饰器内部也是通过调用add_url_route()方法实现的路由注册。
但是显然,使用装饰器使代码看起来更优雅一些。

在示例代码中,注册一个新的路由,当用户访问URL/friend时,返回如下结果: <h1>My Friends List</h1>

为路由指定HTTP方法

默认情况下,Flask路由仅支持HTTP的GET请求。可以使用methods关键字参数,在注册
路由时显式地声明视图方法支持的HTTP方法。

例如,下面的示例将URL规则/auth绑定到视图函数v_auth(),这个路由仅支持POST方法:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/auth’</span><span class="pun">,</span><span class="pln">methods</span><span class="pun">=[</span><span class="str">’POST’</span><span class="pun">])</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_auth</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

指定多种HTTP方法支持

关键字参数methods的类型为list,因此可以同时指定多种HTTP方法。

下面的示例中,使URL规则/user同时支持POST方法和GET方法:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/user’</span><span class="pun">,</span><span class="pln">methods</span><span class="pun">=[</span><span class="str">’POST’</span><span class="pun">,</span><span class="str">’GET’</span><span class="pun">])</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_users</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">if</span><span class="pln"> request</span><span class="pun">.</span><span class="pln">method </span><span class="pun">==</span><span class="pln"> </span><span class="str">’GET’</span><span class="pun">:</span>
        </li>

        <li class="L3">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="pun">...</span><span class="pln"> </span><span class="com"># 返回用户列表</span>
        </li>

        <li class="L4">
            <span class="pln"> </span><span class="kwd">if</span><span class="pln"> request</span><span class="pun">.</span><span class="pln">method </span><span class="pun">==</span><span class="pln"> </span><span class="str">’POST’</span>
        </li>

        <li class="L5">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="pun">...</span><span class="pln"> </span><span class="com">#创建新用户</span>
        </li>

    </ol>

这个特性使Flask非常易于开发REST架构的后台服务,而不仅仅局限于传统的动态网页。

修改示例代码,使URL规则/auth同时支持POST方法和GET方法。

匹配动态URL

有时我们需要将同一类URL映射到同一个视图函数处理,比如,使用同一个视图函数
来显示不同用户的个人档案。我们希望以下的URL都可以分发到同一个视图函数:

Flask简介

在Flask中,可以将URL中的可变部分使用一对小括号<>声明为变量,
并为视图函数声明同名的参数:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/user/<uname>’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_user</span><span class="pun">(</span><span class="pln">uname</span><span class="pun">):</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’%s’s Profile’</span><span class="pln"> </span><span class="pun">%</span><span class="pln"> uname</span>
        </li>

        <li class="L3">
            <span class="pun"></</span><span class="pln">uname</span><span class="pun">></span>
        </li>

    </ol>

在上面的示例中,URL规则中的<uname>表示这部分是可变的,Flask将提取用户请求的
URL中这部分的内容,并作为视图函数v_user()uname参数进行调用:

注册一个新的路由,实现通过URL/user/<uname>/friend/<fname>访问
指定用户的指定朋友的个人信息。

例如,当访问/user/Mary/friend/Linda时,应当返回Mary’s friend – Linda’s profile

URL变量类型过滤

考虑下面的示例,我们希望通过HTTP共享文件夹/var/readonly中的文件:

    <ol class="linenums">
        
        <li class="L0">
            <span class="str">/var</span>
        </li>

        <li class="L1">
            <span class="str"> /</span><span class="kwd">readonly</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="pun">/</span><span class="pln">a</span><span class="pun">.</span><span class="pln">txt</span>
        </li>

        <li class="L3">
            <span class="pln"> </span><span class="pun">/</span><span class="pln">b</span><span class="pun">.</span><span class="pln">txt</span>
        </li>

        <li class="L4">
            <span class="pln"> </span><span class="pun">/</span><span class="pln">repo</span>
        </li>

        <li class="L5">
            <span class="pln"> </span><span class="pun">/</span><span class="pln">c</span><span class="pun">.</span><span class="pln">txt</span>
        </li>

        <li class="L6">
            <span class="pln"> </span><span class="pun">/</span><span class="pln">d</span><span class="pun">.</span><span class="pln">txt</span>
        </li>

    </ol>

简单思考一下就有答案了。我们可以构造URL规则/file/<fname>,然后直接
读取文件内容返回给用户。注册如下的路由:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/file/<fname>’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_file</span><span class="pun">(</span><span class="pln">fname</span><span class="pun">):</span>
        </li>

        <li class="L2">
            <span class="pln"> fullname </span><span class="pun">=</span><span class="pln"> os</span><span class="pun">.</span><span class="pln">path</span><span class="pun">.</span><span class="pln">join</span><span class="pun">(</span><span class="str">’/var/readonly’</span><span class="pun">,</span><span class="pln">fname</span><span class="pun">)</span>
        </li>

        <li class="L3">
            <span class="pln"> f </span><span class="pun">=</span><span class="pln"> open</span><span class="pun">(</span><span class="pln">fullname</span><span class="pun">)</span>
        </li>

        <li class="L4">
            <span class="pln"> cnt </span><span class="pun">=</span><span class="pln"> f</span><span class="pun">.</span><span class="pln">read</span><span class="pun">()</span>
        </li>

        <li class="L5">
            <span class="pln"> f</span><span class="pun">.</span><span class="pln">close</span><span class="pun">()</span>
        </li>

        <li class="L6">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> cnt</span>
        </li>

        <li class="L7">
            <span class="pun"></</span><span class="pln">fname</span><span class="pun">></span>
        </li>

    </ol>

测试结果表明,/file/a.txt和/file/b.txt都没有问题,但是/file/repo/c.txt和
/file/repo/d.txt却会失败。

这是因为,默认情况下,在URL规则中的变量被视为不包含/的字符串。/file/repo/c.txt 是没有办法匹配URL规则/file/<fname>的。

可以使用内置的path转换器告诉Flask框架改变这一默认行为。path转换器允许
规则匹配包含/的字符串:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/file/<path:fname>’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="pun"></</span><span class="pln">path</span><span class="pun">:</span><span class="pln">fname</span><span class="pun">></span>
        </li>

    </ol>

在Flask中,转换器/converter用来对从URL中提取的变量进行预处理,这个过程
发生在调用视图函数之前。Flask预置了四种转换器:

  • string – 匹配不包含/的字符串,这是默认的转换器
  • path – 匹配包含/的字符串
  • int – 只有当URL中的变量是整型值时才匹配,并将变量转换为整型
  • float – 只有当URL中的变量是浮点值时才匹配,并将变量转换为浮点型

在示例代码中注册新的路由,实现计算两个整型值的计算。

例如,当访问URL/add/3/4时,应当返回7,当访问/sub/10/6时,应当返回4

访问点/endpoint

我们一直强调,路由的作用是根据请求的URL,找到对应的视图函数。这没错,但是在
Flask框架中,请求任务的分发并不是直接从用户请求的URL一步定位到视图函数,
两者之间隔着一个访问点/endpoint

以下面的代码为例,我们看Flask怎样实现请求的分发:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/home’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> home</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

在Flask内部使用两张表维护路由:

  • url_map :维护URL规则和endpoint的映射
  • view_functions :维护endpoint和视图函数的映射。

以用户访问URL/home为例,Flask将首先利用url_map找到所请求URL对应的
endpoint,即访问点home,然后再利用view_functions表查找home这个访问点
对应的视图函数,最终匹配到函数home()

Flask简介

默认访问点 :当我们使用route装饰器注册路由时,默认使用被装饰函数的
函数名(__name__)作为访问点,因此,你看到上面的表中,路由中的访问点为home

自定义访问点 :可以在使用route装饰器或调用add_url_rule()方法注册路由时,使用 endpoint关键字参数改变这一默认行为:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/home’</span><span class="pun">,</span><span class="pln">endpoint</span><span class="pun">=</span><span class="str">’whocare’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> home</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

此时的两张路由表将变成这样:

Flask简介

将示例代码中的两个路由的访问点分别改为ep_indexep_about,然后打印 url_mapview_functions,查看有什么变化。

思考一下,改变路由的访问点,对于我们通过URL访问应用,是否有影响?

静态目录路由

当创建应用实例时,Flask将自动添加一条静态目录路由,其访问点 始终被设置为static,URL规则默认被设置为/static,本地路径默认被
设置为应用文件夹下的static子文件夹:

    <ol class="linenums">
        
        <li class="L0">
            <span class="pun">+------------------------------------------------------------+</span>
        </li>

        <li class="L1">
            <span class="pun">|</span><span class="pln"> url rule </span><span class="pun">|</span><span class="pln"> endpoint </span><span class="pun">|</span><span class="pln"> view_function </span><span class="pun">|</span>
        </li>

        <li class="L2">
            <span class="pun">|------------------------------------------------------------|</span>
        </li>

        <li class="L3">
            <span class="pun">|</span><span class="pln"> </span><span class="pun">/</span><span class="kwd">static</span><span class="pln"> </span><span class="pun">|</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="pun">|</span><span class="pln"> </span><span class="typ">Flask</span><span class="pun">.</span><span class="pln">send_static_file </span><span class="pun">|</span>
        </li>

        <li class="L4">
            <span class="pun">+------------------------------------------------------------+</span>
        </li>

    </ol>

如果你的应用目录如下:

    <ol class="linenums">
        
        <li class="L0">
            <span class="pln">/app</span>
        </li>

        <li class="L1">
            <span class="pln"> /web.py</span>
        </li>

        <li class="L2">
            <span class="pln"> /static</span>
        </li>

        <li class="L3">
            <span class="pln"> /main.css</span>
        </li>

        <li class="L4">
            <span class="pln"> /jquery.min.js </span>
        </li>

    </ol>

那么启动应用后就可以通过URL/static/main.css访问static文件夹下的main.css了。

除了访问点被固定为static,静态目录的URL规则本地目录都是可以根据应用情况进行调整。

改变默认的本地路径 :可以在创建应用对象时使用关键字参数static_folder改变
默认的静态文件夹。例如,你的静态文件都存放在应用下的assets目录下,
那么可以按如下的方式创建应用对象:

    <ol class="linenums">
        
        <li class="L0">
            <span class="pln">app </span><span class="pun">=</span><span class="pln"> </span><span class="typ">Flask</span><span class="pun">(</span><span class="pln">__name__</span><span class="pun">,</span><span class="pln">static_folder</span><span class="pun">=</span><span class="str">’assets’</span><span class="pun">)</span>
        </li>

    </ol>

也可以使用一个绝对路径:

    <ol class="linenums">
        
        <li class="L0">
            <span class="pln">app </span><span class="pun">=</span><span class="pln"> </span><span class="typ">Flask</span><span class="pun">(</span><span class="pln">__name__</span><span class="pun">,</span><span class="pln">static_folder</span><span class="pun">=</span><span class="str">’/var/www/static’</span><span class="pun">)</span>
        </li>

    </ol>

改变默认的本地路径并不会对路由表产生影响。

改变默认的URL规则 : 如果不喜欢静态目录URL/static,也可以在创建应用
对象时使用关键字参数static_url_path换一个别的名字。

下面的示例中,将应用下的assets文件夹注册为静态目录/assets

    <ol class="linenums">
        
        <li class="L0">
            <span class="pln">app </span><span class="pun">=</span><span class="pln"> </span><span class="typ">Flask</span><span class="pun">(</span><span class="pln">__name__</span><span class="pun">,</span><span class="pln">static_folder</span><span class="pun">=</span><span class="str">’assets’</span><span class="pun">,</span><span class="pln">static_url_path</span><span class="pun">=</span><span class="str">’/assets’</span><span class="pun">)</span>
        </li>

    </ol>

当应用运行后,通过URL/assets/main.css就可以访问assets文件夹下的
main.css文件了。

这时的路由表变化为:

    <ol class="linenums">
        
        <li class="L0">
            <span class="pun">+------------------------------------------------------------+</span>
        </li>

        <li class="L1">
            <span class="pun">|</span><span class="pln"> url </span><span class="pun">|</span><span class="pln"> endpoint </span><span class="pun">|</span><span class="pln"> view_function </span><span class="pun">|</span>
        </li>

        <li class="L2">
            <span class="pun">|------------------------------------------------------------|</span>
        </li>

        <li class="L3">
            <span class="pun">|</span><span class="pln"> </span><span class="pun">/</span><span class="pln">assets </span><span class="pun">|</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="pun">|</span><span class="pln"> </span><span class="typ">Flask</span><span class="pun">.</span><span class="pln">send_static_file </span><span class="pun">|</span>
        </li>

        <li class="L4">
            <span class="pun">+------------------------------------------------------------+</span>
        </li>

    </ol>

练习1. 将应用的静态目录指向应用目录下的assets子目录

练习2. 将应用的静态目录URL修改为/mylib

在两种情况下,分别查看路由表url_mapview_functions,思考这两种操作对
路由表的影响和对访问点的影响。

构造URL

在一个实用的视图中,不可避免地存在指向其他视图的链接。在之前的课程示例中,我们
都是在视图函数中这样硬编码这些链接URL的:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_index</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’<a href="/tech">tech</a>’</span>
        </li>

        <li class="L3">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/tech’</span><span class="pun">)</span><span class="pln"> </span>
        </li>

        <li class="L4">
            <span class="kwd">def</span><span class="pln"> v_tech</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

大部分情况下这种硬编码URL是可以工作的。但如果这个应用被挂在WSGI服务器的一个
子路径下,比如:/app1,那么用户访问URL/tech是不会成功的,这时应当访问/app1/tech 才可以正确地路由到视图函数v_tech()

我们应当使用访问点让Flask框架帮我们计算链接URL。简单地给url_for()函数传入
一个访问点,它返回将是一个可靠的URL地址:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_index</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">print</span><span class="pln"> url_for</span><span class="pun">(</span><span class="str">’v_contacts’</span><span class="pun">)</span><span class="pln"> </span><span class="com"># /contact</span>
        </li>

        <li class="L3">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’see console output!’</span>
        </li>

        <li class="L4">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/contact’</span><span class="pun">)</span>
        </li>

        <li class="L5">
            <span class="kwd">def</span><span class="pln"> v_contacts</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

添加查询参数 : 使用关键字参数,可以在构造的URL中生成查询串。下面的调用将生成 /contact?format=json

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_index</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">print</span><span class="pln"> url_for</span><span class="pun">(</span><span class="str">’v_contacts’</span><span class="pun">,</span><span class="pln">format</span><span class="pun">=</span><span class="str">’json’</span><span class="pun">)</span>
        </li>

        <li class="L3">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’’</span>
        </li>

        <li class="L4">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/contact’</span><span class="pun">)</span><span class="pln"> </span>
        </li>

        <li class="L5">
            <span class="kwd">def</span><span class="pln"> v_contacts</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

添加URL变量 : 如果指定访问点对应的视图函数接收参数,那么关键字参数将生成对应的参数URL。下面的
示例将生成/contact/Julia?format=html

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_index</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">print</span><span class="pln"> url_for</span><span class="pun">(</span><span class="str">’v_contact’</span><span class="pun">,</span><span class="pln">name</span><span class="pun">=</span><span class="str">’Julia’</span><span class="pun">,</span><span class="pln">format</span><span class="pun">=</span><span class="str">’html’</span><span class="pun">)</span>
        </li>

        <li class="L3">
            <span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="str">’’</span>
        </li>

        <li class="L4">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/contact/<name>’</span><span class="pun">)</span>
        </li>

        <li class="L5">
            <span class="kwd">def</span><span class="pln"> v_contact</span><span class="pun">(</span><span class="pln">name</span><span class="pun">):</span><span class="kwd">pass</span>
        </li>

        <li class="L6">
            <span class="pun"></</span><span class="pln">name</span><span class="pun">></span>
        </li>

    </ol>

添加锚点 :使用_anchor关键字可以为生成的URL添加锚点。下面的示例将生成URL /contact#part2

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_index</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">print</span><span class="pln"> url_for</span><span class="pun">(</span><span class="str">’v_contacts’</span><span class="pun">,</span><span class="pln">_anchor</span><span class="pun">=</span><span class="str">’part2’</span><span class="pun">)</span>
        </li>

        <li class="L3">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/contact’</span><span class="pun">)</span>
        </li>

        <li class="L4">
            <span class="kwd">def</span><span class="pln"> v_contacts</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

外部URL : 默认情况下,url_for()生成站内URL,可以设置关键字参数_external 为True,生成包含站点地址的外部URL。下面的示例将生成URLhttp://<x.y.z>/contacts:

    <ol class="linenums">
        
        <li class="L0">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/’</span><span class="pun">)</span>
        </li>

        <li class="L1">
            <span class="kwd">def</span><span class="pln"> v_index</span><span class="pun">():</span>
        </li>

        <li class="L2">
            <span class="pln"> </span><span class="kwd">print</span><span class="pln"> url_for</span><span class="pun">(</span><span class="str">’v_contacts’</span><span class="pun">,</span><span class="pln">_external</span><span class="pun">=</span><span class="kwd">True</span><span class="pun">)</span>
        </li>

        <li class="L3">
            <span class="lit">@app</span><span class="pun">.</span><span class="pln">route</span><span class="pun">(</span><span class="str">’/contact’</span><span class="pun">)</span>
        </li>

        <li class="L4">
            <span class="kwd">def</span><span class="pln"> v_contacts</span><span class="pun">():</span><span class="kwd">pass</span>
        </li>

    </ol>

使用url_for()修改示例代码:

1. 为访问点v_contacts生成URL:/contact?format=json&page=1

2. 为访问点v_contact生成URL:/contact/whoami?format=xml

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