完成登录功能，用session记住用户名

登录功能完成：

1. js:设置return
2. html:设置
   1. form
   2. input
3. py:
   1. @app.route设置methods
   2. GET
   3. POST
      1. 读取表单数据
      2. 查询数据库
         1. 用户名密码对：
            1. 记住用户名
            2. 跳转到首页
         2. 用户名密码不对：
            1. 提示相应错误。

js:

function fnLogin() {
         var oUname = document.getElementById("uname");
         var oError = document.getElementById("error-box");
         var oUpass = document.getElementById("upass");
         var oUpass1 = document.getElementById("upass1");
         var isoError = true;
         oError.innerHTML = "<br>";

         if (oUname.value.length<6||oUname.value.length>20){
              oError.innerHTML="用户名要6-20位";
              isoError = false;
              return;
                }
                else if(oUname.value.charCodeAt(0)>=48&&(oUname.value.charCodeAt(0)<=57)){
             oError.innerHTML = "用户名首位必须为字母";
             isoError = false;
             return;
         }else for(var i=0;i<oUname.value.length;i++){
                if((oUname.value.charCodeAt(i)<48||oUname.value.charCodeAt(i)>57)&&(oUname.value.charCodeAt(i)<97||oUname.value.charCodeAt(i)>122)){
                    oError.innerHTML = "用户名必须为字母或数字";
                    isoError = false;
                    return;
                }
         }


          if (oUpass.value.length<6||oUpass.value.length>20){
                    oError.innerHTML="密码至少6-20位";
                     isoError = false;
                      return;

            }
            if (oUpass1.value!=oUpass.value){
                      oError.innerHTML="密码不一致,请重新输入";
                      isoError = false;
                      return;
            }
             return isoError;
             return window.alert("注册成功！")
        }

html:

{% extends 'base.html' %}
{% block title %}
    login
{% endblock  %}

{% block head %}

    <link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='css/10.31.css') }}">
    <script src="{{ url_for('static',filename='js/10.31.js') }}"></script>

{% endblock  %}

{% block main %}
<div class="box">
    <div id="title">LoginText</div>
    <h3>登录</h3>
    <form action="{{ url_for('login') }}" method="post">
    <div class="input-box">
        账号：<input id="uname" type="text" name="username" placeholder="请输入用户名">
    </div>
    <div class="input-box">
        密码：<input id="upass" type="password" name="password" placeholder="请输入密码">
    </div>
    <div id="error-box"><br></div>
    <div class="input-box">
        <button onclick="fnLogin()">登录</button>
        <a href="{{ url_for('register') }}">注册/Register</a>
    </div>
        </form>
</div>

{% endblock  %}

py:

@app.route('/login',methods=['GET','POST'])
def login():
    if request.method == 'GET':
       return render_template('login.html')
    else:
        usern = request.form.get('username')
        passw = request.form.get('password')
        user = User.query.filter(User.username == usern).first()
        if user:
            if user.password == passw:
                session['user'] = usern
                session.permanent = True
                return redirect(url_for('index'))  # 重定向到首页
            else:
                return u'password error'
        else:
            return u'username is not existed'

session：

1. 从`flask`中导入`session`

   from flask import render_template,redirect,url_for,request,session

2. 设置`SECRET_KEY`

   import os
   
   SELECT_KEY = os.urandom(24)

3. 操作字典一样操作`session`：增加用户名`session['username']=`username

    session['user'] = usern
    session.permanent = True