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 oUpass=document.getElementById("upass");
                    var oError=document.getElementById("error_box");
                    var isError=true;
                    oError.innerHTML="<br>"
                    if(oUname.value.length<6|| oUname.value.length > 20){
                        oError.innerHTML="用户名至少6-20位";
                        isError=false;
                        return isError;
                    }else if((oUname.value.charCodeAt(0)>=48) && (oUname.value.charCodeAt(0)<=57)){
                        oError.innerHTML="first letter.";
                        isError = false;
                        return isError;
                    }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";
                            isError = false;
                            return isError;
                        }
                    }
                    if(oUpass.value.length<6|| oUpass.value.length > 20){
                        oError.innerHTML="密码至少6-20位"
                        isError = false;
                        return isError;
                    };
                    return isError;
                    window.alert("登录成功！")
                }

               html:

               {% extends'index.html' %}
               
               {% block title %}登录 {% endblock %}
               
               {% block head %}
                <link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='css/886.css') }}">
                   <script src="{{ url_for('static',filename='js/tt.js')}}"></script>
               {% endblock %}
               
               {% block main %}
                <div class="box">
                        <h2 class="dd">登录</h2>
                        <form action="{{url_for('login')}}" method="post">
                        <div class="input_box">
                            <input id="uname" type="text" placeholder="请输入用户名" name="username">
                        </div>
                        <div class="input_box">
                            <input id="upass" type="password" placeholder="请输入密码" name="password">
                        </div>
                        <div id="error_box"><br></div>
                        <div>
                            <button class="jj" onclick="fnLogin()">登录</button>
                       </div>
                        </form>
                    </div>
               {% endblock %}

               py:

               from flask import Flask,render_template,request,redirect,url_for,session
               from flask_sqlalchemy import SQLAlchemy
               import config
               from functools import wraps
               from datetime import datetime
               
               
               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(50))
               
               
               # db.create_all()
               # 增加
               # user = User(username='mis1114',password = 'mis1114',nickname='mis1114')
               # db.session.add(user)
               # db.session.commit()
               # # 查询
               # User.query.filter(User.username == 'mis1114').first()
               # #修改
               # user =User.query.filter(User.username =='mis1114').first()
               # user.password='23456'
               # print(user.username,user.password)
               # db.session.commit()
               # # 删除
               # user =User.query.filter(User.username =='mis1114').first()
               # db.session.delete(user)
               # db.session.commit()
               
               
               @app.route('/')
               def index():
                   return render_template('index.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,User.password==password).first()
                       if user:
                           session['user']=username
                           session.permanent=True
                           return redirect(url_for('index'))
                       else:
                           return u'error username or password'
               
               
               @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('/question/')
               def question():
                   return render_template('question.html')
               
               if __name__ == '__main__':
                   app.run(debug=True)