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。

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

   function fnLogin() {
       var uSer = document.getElementById("user");
       var pAss = document.getElementById("pass");
       var oError = document.getElementById("error_box");
       oError.innerHTML = "<br>";
       if (uSer.value.length < 6 || uSer.value.length > 20) {
           oError.innerHTML = "请输入6-20位用户名";
           return
       } else if ((uSer.value.charCodeAt(0) >= 48) && (uSer.value.charCodeAt(0) <= 57)) {
           oError.innerHTML = "用户名首字不能是数字";
           return
       } else for (var i = 0; i < uSer.value.length; i++) {
           if ((uSer.value.charCodeAt(i) < 48) || (uSer.value.charCodeAt(i) > 57) && (uSer.value.charCodeAt(i) < 97) || (uSer.value.charCodeAt(i) > 122)) {
               oError.innerHTML = "用户名只能是数字和字母";
               return
           }
       }
   
       if (pAss.value.length < 6 || pAss.value.length > 20) {
           oError.innerHTML = "请输入6-20位密码";
           return
       }
       // 验证弹框
       window.alert("成功")
   }
   
   
   function fnRegistration() {
       var uSer = document.getElementById("user");
       var pAss = document.getElementById("pass");
       var aGain = document.getElementById("again");
       var oError = document.getElementById("error_box");
   
       oError.innerHTML = "<br>";
   
       // 验证用户名
       if (uSer.value.length < 6 || uSer.value.length > 20) {
           oError.innerHTML = "请输入6-20位用户名";
           return
       } else if ((uSer.value.charCodeAt(0) >= 48) && (uSer.value.charCodeAt(0) <= 57)) {
           oError.innerHTML = "用户名首字不能是数字";
           return
       } else for (var i = 0; i < uSer.value.length; i++) {
           if ((uSer.value.charCodeAt(i) < 48) || (uSer.value.charCodeAt(i) > 57) && (uSer.value.charCodeAt(i) < 97) || (uSer.value.charCodeAt(i) > 122)) {
               oError.innerHTML = "用户名只能是数字和字母";
               return
           }
       }
   
       // 验证密码
       if (pAss.value.length < 6 || pAss.value.length > 20) {
           oError.innerHTML = "请输入6-20位密码";
           return
       }
   
       // 验证再次输入的密码
       if (aGain.value != pAss.value) {
           oError.innerHTML = "请输入相同的密码";
           return
       }
       // 验证弹框
       window.alert("成功")
   }

   PY:

   from flask import Flask, render_template, url_for, redirect, request
   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)
       nickname = db.Column(db.String(20))
   
   
   db.create_all()
   
   
   # 增加
   # user = User(username='tan1997',password='19961021')
   # db.session.add(user)
   # db.session.commit()
   
   # 查询
   # user = User.query.filter(User.username == 'tan1997').first()
   # print(user.username,user.password)
   
   # 修改
   # user=User.query.filter(User.username == 'tan1997').first()
   # user.password=1234567
   # db.session.commit()
   
   # 删除
   # user=User.query.filter(User.username == 'tan1997').first()
   # db.session.delete(user)
   # db.session.commit()
   
   @app.route('/')
   def myweb():
       return render_template("denglu.html")
   
   
   @app.route('/login/', methods=['GET', 'POST'])
   def login():
       if request.method == 'GET':
           return render_template("zhuce.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:
                   return redirect(url_for('myweb'))
               else:
                   return '错误'
           else:
               return '用户不存在'
   
   
   
   @app.route('/regist/', methods=['GET', 'POST'])
   def regist():
       if request.method == 'GET':
           return render_template("zhuce.html")
       else:
           username = request.form.get('username')
           password = request.form.get('password')
           nickname = request.form.get('nickname')
           user = User.query.filter(User.username == username).first()
           if user:
               return '用户已存在'
           else:
               user = User(username=username, password=password, nickname=nickname)
               db.session.add(user)  # 数据库，添加操作
               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)

   HTML:

   {% extends 'daohang.html' %}
   
   {% block denglutitle %}登陆{% endblock %}
   {% block dengluhead %}
       <link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='css/denglu.css') }}">
       <script src="{{ url_for('static',filename='js/text.js') }}"></script>
   {% endblock %}
   {% block denglubody %}
      <div id="container">
       <div id="header"><h2 align="center">登录</h2></div>
       <div id="content">
           <form>
               账号：<input type="text" name="user" id="user" placeholder="输入用户名">
               <br>
               密码：<input type="password" name="pass" id="pass" placeholder="输入密码">
               <input type="checkbox" name="c1" id="c1" value="">记住账号
               <br>
               <div id="error_box"><br></div>
               <input type="button" value="登录" onclick="fnLogin()">&nbsp
   
   
   
           </form>
       </div></div>
   
   
   {% endblock %}

   import os
   DEBUG = True
   
   SECRET_KEY = os.urandom(24)
   
   DIALECT = 'mysql'
   DRIVER = 'mysqldb'
   USERNAME = 'root'
   PASSWORD = 'ROOT'
   HOST = '127.0.0.1'
   DATABASE = 'mytest'
   
   
   SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:@127.0.0.1:3306/mytest?charset=utf8'
   SQLALCHEMY_TRACK_MODIFICATIONS = False