登录功能完成：

1. js:设置return
2. html:设置
   1. form
   2. input

   3. οnclick="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,sessionfrom flask_sqlalchemy import SQLAlchemyimport configapp = Flask(__name__)app.config.from_object(config)db=SQLAlchemy(app)class User(db.Model):    __table__name = '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(50))db.create_all()@app.route('/')def index():    return render_template('index.html')@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')        nickname=request.form.get('nickname')        user=User.query.filter(User.username==username).first()        if user:            return u'username existed'        else:            user=User (username=username,password=password,nickname=nickname)            db.session.add(user)            db.session.commit()            return redirect(url_for('login'))@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                return redirect(url_for('index'))            else:                return u'password error'        else:            return u'username is not existed'if __name__ == '__main__':    app.run(debug=True)
   import osSECRET_KEY = os.urandom(24)SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:@localhost:3306/mis_db?charset=utf8'SQLALCHEMY_TRACK_MODIFICATIONS = False
   {% extends 'base.html' %}{% block title %}登录{% endblock %}{% block head %}    
               {% endblock %}{% block main %}
           
       
            
             
   LOGIN
            
       
            
       
             
                      Username：
              
              
           Password：
              
              
           
             
           
             
              
             
         
             
            
              Login         
              Cancel    
             
           
            
           
   {% endblock %}
   function myLogin(){            var uName=document.getElementById("name");            var uError=document.getElementById("error_box");            var upass = document.getElementById("password");            var isError=true;            uError.innerHTML = "
   "            //uname            if(uName.value.length>12 || uName.value.length<6){                uError.innerHTML="Username 6-12 bits";                isError=false;                return isError;            }else if((uName.value.charCodeAt(0)>=48)&& uName.value.charCodeAt(0)<=57){                uError.innerHTML="The first letter cannot be numeric";                isError=false;                return isError;            }else for(var i=0; i
           
            57)&&(uName.value.charCodeAt(i)<97 || uName.value.charCodeAt(i)>122 )){                    uError.innerHTML = "only letter or number.";                    isNotError=false;                    return isError;                }            }            if(upass.value.length>12 || upass.value.length<6){                uError.innerHTML="password 6-12 bits";                isError=false;                return isError;            }            return isError;        }
           

    

4.