Flask表单疑问，这个name是怎么传进来的？
回复内容：
泻药！没看form有关的源码，但是应该是这样的∶
首先，你得理解像flask这种MVC（或者说MTC）的基本运行机制。
- 对于flask的view，你得知道wsgi协议（如果不清楚，请自行Google之）。
更底层（逻辑上的底层）的HTTP utils（flask用的是werkzeug）将client端的HTTP requests等进行parse，并且将其构建为wsgi的environment（包含了request及其他信息）。
wsgi server在process请求的过程是：根据wsgi协议构建environ，将其传入flask app instance（这个即为flask框架实现的wsgi app），flask app instance用这个environ和自己的``start_response`` method（这个也是uwsgi协议规约）完成请求处理并response。
flask有一个线程级（或greenlet）的request对象。在真正process response之前，将environ丢到这个request对象里，之后这个request跟着你的那个线程就成为了默契的炮友~~直至response完成或线程完蛋。
views里面的那一坨坨的route的作用是啥捏？这个就是url routing了，就是我在你的站点上点了一个特定的url，flask要如何满足你。你得说出你想要的东西吧。
那么views是什么时候用到呢？废话，当然还是在接收并理解请求之后到响应之前。
好了，flask app instance在处理你的需求的时候从request对象里拿到了你请求的url，这个就相当于一把key，然后app instance根据这个key去views里找到了对应的锁（你想要的处理逻辑，就是views里的route下面的function），这个锁啊，她一旦被打开了，满足你需求的时刻也就快了 ~ ~
P.S. 至于如何匹配到这个锁的呢，这个就是url mapping了，就是一堆正则匹配（别小看这个，如果你用过flask的blueprint，你会明白写这么个mapping也是件爽hi了的事情咯）
- model & controller呢？
你的需求其实就是要flask给你response，response其实呢就是数据（不管是RESTFUL API还是template形式，都是你撸出的data）。
数据这坨翔实怎么来的呢？就是你从数据库（广义，包括sql & nosql db，内存级缓存，磁盘文件等等等等）拿到的，至于data的来源嘛，可能是你自己插的，或者是从别的地方哭着要来的。
model就是干这活的，只不过它比较抽象，将数据库操作转成了对Python对象的操作（这个就是大名鼎鼎的ORM，其实并没有什么卵用，ORM写多了你连查询优化都忘了，如果你有比较高的performance需求也有很多时间，就自己撸高效检索方案吧，我没少被这玩意儿坑%>_
controller这玩意儿你其实可以不要，不过为了做逻辑分离，让你撸业务撸的漂亮点儿还是用它吧。
OK，说了这么多，不知道有没有人能看懂，如果没看懂，让我思考会儿吧 ~ ~
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简而言之呢，你用flask作application的时候，MVC各司其职堆好你产生data的逻辑即可，其它你一概不用管。
靠，终于可以回到你的问题上了：
先看下Form这玩意儿：
from flask.ext.wtf import Form
from wtforms import StringField, SubmitField
from wtforms.validators import Required
class NameForm(Form):
name = StringField('What is your name?', validators=[Required()])
submit = SubmitField('Submit')
<span class="err">我当初也被搞糊涂了，那本</span> <span class="n">flask</span> <span class="n">web</span> <span class="n">development</span><span class="err">里用到的是</span><span class="n">flask_wtf</span><span class="err">模块，而有的教程里用到的却是</span><span class="n">WTForms</span><span class="err">模块。</span>
<span class="err">这是</span><span class="n">WTForms</span><span class="err">的表单验证路由函数</span>
<span class="nd">@app.route</span><span class="p">(</span><span class="s">'/register'</span><span class="p">,</span> <span class="n">methods</span><span class="o">=</span><span class="p">[</span><span class="s">'GET'</span><span class="p">,</span> <span class="s">'POST'</span><span class="p">])</span>
<span class="k">def</span> <span class="nf">register</span><span class="p">():</span>
<span class="n">form</span> <span class="o">=</span> <span class="n">RegistrationForm</span><span class="p">(</span><span class="n">request</span><span class="o">.</span><span class="n">form</span><span class="p">)</span>
<span class="k">if</span> <span class="n">request</span><span class="o">.</span><span class="n">method</span> <span class="o">==</span> <span class="s">'POST'</span> <span class="ow">and</span> <span class="n">form</span><span class="o">.</span><span class="n">validate</span><span class="p">():</span>
<span class="k">pass</span>
<span class="err">对比二者你会发现，二者有三个区别</span>
<span class="mf">1.</span><span class="n">RegistrationForm</span><span class="err">实例化时用到了</span><span class="n">request</span><span class="o">.</span><span class="n">form</span><span class="err">，而你的例子里没有用到。</span>
<span class="mf">2.</span><span class="err">你的例子里没有验证表单是</span><span class="n">POST</span><span class="err">还是</span><span class="n">GET</span><span class="err">方法，上面这个例子里用了</span><span class="n">request</span><span class="o">.</span><span class="n">method</span> <span class="o">==</span> <span class="s">'POST'</span>
<span class="mf">3.</span><span class="err">一个是</span><span class="n">form</span><span class="o">.</span><span class="n">validate</span><span class="p">()</span><span class="err">，一个是</span><span class="n">form</span><span class="o">.</span><span class="n">validate_on_submit</span><span class="p">()</span><span class="err">。</span>
<span class="err">可见</span><span class="n">flask_wtf</span><span class="err">模块里的</span><span class="n">Form</span> <span class="err">类对</span><span class="n">WTForms</span><span class="err">里的</span><span class="n">Form</span><span class="err">类进行了封装。</span>
<span class="err">把</span><span class="n">request</span><span class="o">.</span><span class="n">form</span> <span class="err">和</span><span class="n">request</span><span class="o">.</span><span class="n">method</span> <span class="o">==</span> <span class="s">'POST'</span><span class="err">封装进去了。对比一下代码应该很容易明白。</span>
1、 当路由触发 index 视图函数。
form = NameForm() 这条语句创建一个form 实例对象，也就是说表单创建了。
2、如果是第一次访问含有这个表单的页面 也就是GET请求
if form.validate_on_submit() 这个判断为假，下面的语句块不执行。
3、如果是POST请求
这个时候，表单已经存在。
if form.validate_on_submit() 这个判断为真，下面的语句块要执行。
name = form.name.data 这条语句在POST的时候，取得form表单属性值。
4、无论POST、还是GET
return render_template('index.html', form=form, name=name)
这条语句都要被执行。
如何取得form表单的值，请看flask.request。
class flask.requestAPI — Flask Documentation (0.10)
To access incoming request data, you can use the global request object. Flask parses incoming request data for you and gives you access to it through that global object. Internally Flask makes sure that you always get the correct data for the active thread if you are in a multithreaded environment.
This is a proxy. See Notes On Proxies for more information.
The request object is an instance of a Request subclass and provides all of the attributes Werkzeug defines. This just shows a quick overview of the most important ones.
可以先看看 @wang Harvey 和 @朱添一 的回答，再去看一下Flask-WTF中定义Form类的源码，在Form类的注释里，https://github.com/lepture/flask-wtf/blob/master/flask_wtf/form.py#L41-L42 这两行应该能够清楚解释题主的问题了。在此引用一下：If formdata is not specified, this will use flask.request.form.
Explicitly pass formdata = None to prevent this.
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== 虽然@wang harvey 的答案非常棒，但我觉得完全没解决楼主的问题啊…………不行，@不上最高票答主了……
楼主不知道 name 是怎么出来的？那么 name 是定义出来的。python是强类型，直接定义了 name 来存储 form.name.data 的数据。
那么 form.name.data 是怎么出来的？form.name是你在 form 里面定义的一个数据，它的 name(参见[文档]Forms — WTForms 2.0.3dev documentation )就是 name(你自己定义的) 。
那么我们把 form.name.data 传给 name ，有什么用呢？我们看它是重定向到 index.html 里面的，那么我们打开 index.html(为了这个我还专门打开好长时间都没用的文件 checkout 了一把)，我们可以看到
<h1 id="Hello-if-name-name-else-Stranger-endif">Hello, {% if name %}{{ name }}{% else %}Stranger{% endif %}!</h1>
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以下是我的个人理解，首先第一次请求的时候，是get请求，渲染了一个空的表格页面，当你填完了东西之后，点击提交就已经是第二次请求，post请求，这时候就把表格的内容发送给服务器，再进行赋值。
题主，我跟你用的同一本书。我是自学程序，看了基本的python语法就强撸这本书了。最开始真的html都不会。。。。。。然后到现在两个月多了，不好意思才看到第六章第七章。。。
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