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. onclick="return fnLogin()"

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。

session：

1. 从`flask`中导入`session`
2. 设置`SECRET_KEY`
3. 操作字典一样操作`session`：增加用户名`session['username']=`username

   from flask import Flask,render_template,request,redirect,url_for,session
   from flask_sqlalchemy import SQLAlchemy
   import config
   
   app = Flask(__name__)
   app.config.from_object(config)
   
   db=SQLAlchemy(app)
   
   class User(db.Model):
       __tablename__ = 'user'
       id = db.Column(db.Integer,primary_key=True,autoincrement=True)
       username = db.Column(db.String(20),nullable=False)
       password = db.Column(db.String(20), nullable=False)
   
   db.create_all()
   
   @app.route('/')
   def base():
       return render_template('base.html')
   
   @app.route('/login/',methods=['GET','POST'])
   def login():
       if request.method=='GET':
           return render_template('login.html')
       else:
           username = request.form.get('username')
           password = request.form.get('password')
           user = User.query.filter(User.username==username).first()
           if user:
               if user.password==password:
                   session['user'] = username
                   session.permanent = True
                   return redirect(url_for('base'))
               else:
                   return 'Password error'
           else:
               return 'Username inexistent'
   
   @app.route('/regist/',methods=['GET','POST'])
   def regist():
       if request.method == 'GET':
           return render_template("regist.html")
       else :
           username = request.form.get('username')
           password = request.form.get('password')
           user = User.query.filter(User.username == username).first()
           if user:
               return 'Username existed'
           else:
               user1 = User(username=username, password=password)
               db.session.add(user1)
               db.session.commit()
               return redirect(url_for('login'))
   
   @app.route('/question/')
   def question():
       return render_template('question.html')
   
   if __name__ == '__main__':
       app.run(debug=True)

   import os
   SECRET_KEY = os.urandom(24)
   
   SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:@localhost:3306/wuwen?charset=utf8'
   SQLALCHEMY_TRACK_MODIFICATIONS = False

   {% extends 'base.html' %}
   
   {% block title %}Login{% endblock %}
   
   {% block head %}
       <link href="{{ url_for('static',filename='CSS/login.css') }}" rel="stylesheet" type="text/css">
       <script src="{{ url_for('static',filename='JScript/login.js') }}"></script>
   {% endblock %}
   
   {% block main %}
   <div class="login">
       <form action="{{ url_for('login') }}" method="post">
           <div class="login-top">
               <h1>LOGIN FORM</h1>
               <input id="uname" name="username" type="text" value="Username" onfocus="this.value = '';" onblur="if (this.value==''){ this.value = 'Username';}">
               <input id="upass" name="password" type="password" value="Password" onfocus="this.value = '';" onblur="if (this.value==''){ this.value = 'Password';}">
               <div class="forgot">
                   <input type="checkbox"><p>Keep me logged in</p>
                   <a href="#">forgot Password</a>
               </div>
           </div>
           <div class="login-bottom">
               <div id="errorbox"></div><button onclick="return MyLogin()">Login</button>
           </div>
       </form>
   </div>
   {% endblock %}

   function MyLogin() {
       var oUname=document.getElementById("uname");
       var oUpass=document.getElementById("upass");
       var oError=document.getElementById("errorbox");
   
       //username
        if(oUname.value=="Username"&&oUpass.value=="Password"){
           oError.innerHTML="Please input username";
           return false;
       }else if(oUname.value.length<6||oUname.value.length>12){
           oError.innerHTML="Username must be 6 to 12";
           return false;
       }else if(oUname.value.charCodeAt(0)>=48 && oUname.value.charCodeAt(0)<=57){
           oError.innerHTML="Frist Letter";
           return false;
       }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 = "Only letter or number";
               return false;
           }
       }
       //password
       if(oUpass.value.length<6||oUpass.value.length>12) {
           oError.innerHTML = "Password must be 6 to 12";
           return false;
       }
       return true;
       // window.alert("Login Successful")
   }