完成登录功能，用session记住用户名

        function muregist() {
            var password=document.getElementById("password");
            var password1=document.getElementById("password");

             if(password!=password1){
         document.getElementById("error_box").innerHTML="两次密码不一致，请重新输入";
         return false;
        }
        return true;
        }

{% extends 'index.html' %}
{% block title %}登录{% endblock %}

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

{% block main %}
<div class="box">
    <h2>登录</h2>
    <br><br>

    <form action="{{url_for('login')}}" method="post">
        <div class="input_box">
            <input id="username" type="text" placeholder="请输入用户名" name="username">
        </div>

        <div class="input_box">
            <input id="password" type="text" placeholder="请输入密码" name="password"><br>
        </div>
        <div id="error_box"><br></div>
        <br>
        <div>
            <button onclick="mulogin()">登录</button>
            <a href="regist.html"></a>
        </div>
    </form>
</div>
{% endblock %}

@app.route('/login/', methods=['GET', 'POST'])
def login():
    if request.method == 'GET':
        return render_template('login.html')
    else:
        username = request.form.get('username')  # 获取form中的数据
        passwrod = request.form.get('passwrod')
        user = User.query.filter(User.username == username ,User.password==passwrod).first()
        if user:
            session['user'] = username
            session.permanent=True
            return redirect(url_for('index'))  # 重新定向到首页
        else:
            return 'ERROR USERNAME OR PASSWROD'  # 返回提示信息

import os
SECRET_KEY = os.urandom(24)