完成登录功能，用session记住用户名

登录功能完成：

js:设置return
html:设置
1. form
2. input
3. ```
onclick="return fnLogin()"
```
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：

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

js:

function myLogin() {
            var oUname=document.getElementById("uname");
            var oPass=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='请输入6-20位的用户名';
                isError=false;
             return isError;

            }
            if(oUname.value.charCodeAt(0)>=48&&oUname.value.charCodeAt(0)<=57){
                oError.innerHTML='首字母不能为数字';

             return isError;
            }else {
                for (var i = 0; i < oUname.value.length; i++) {
                    if ((oUname.value.charCodeAt(i) > 122 || oUname.value.charCodeAt(i) < 97) && (oUname.value.charCodeAt(i) > 57 && oUname.value.charCodeAt(i) < 48)) {
                        oError.innerHTML = '只能输入字母或数字';
                        isNotError = false;
                        return isError;
                    }
                }
            }
            if(oPass.value.length<6||oPass.value.length>20) {
                oError.innerHTML = '请输入6-20位的密码';
                return isError;

            }

        }
function mySwitch() {
    var myele=document.getElementById("on_off")
    if(myele.src.match("u=1878009223,3806655311&fm=200&gp=0"))
    {
        myele.src="https://www.duitang.com/blog/?id=528606516"
        document.getElementById("myBody").style.background="gray"
        document.getElementById("demo").style.color="white"


    }else{
        myele.src="https://www.duitang.com/blog/?id=528606516";
        document.getElementById("myBody").style.background="white"
        document.getElementById("demo").style.color="gray"
    }

}

{% extends 'index.html' %}
<head>
    <meta charset="UTF-8">
    <title>{% block title %}sign_in {% endblock %}</title>
    {% block head %}
    <link  href="{{ url_for('static',filename='css/nino.css') }}" rel="stylesheet" type="text/css" >
    <script src="{{ url_for('static',filename='js/sign_in.js') }}"></script>
    {% endblock %}
</head>
<body>

    {% block main %}
    <div class="box">
        <h2>登录</h2>
         <form class="form" method="post" action="{{ url_for('sign_in') }}">

        <div class="input_box">
            <input id="uname" class="sign" type="text" placeholder="请输入用户名" name="username">
        </div>
        <div class="input_box">
            <input id="upass" class="sign" type="password" placeholder="请输入密码" name="password">
        </div>

        <div id="error_box"><br>
        </div>
        <div class="input_box">
            <input type="submit" name="commit" value="登录" class="sign-in-button" data-disable-with="登录" onclick="myLogin()">

            </div>
         </form>
        </div>

{% endblock %}
</body>

config:

import os

SECRET_KEY = os.urandom(24)

SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:@127.0.0.1:3306/test?charset=utf8'
SQLALCHEMY_TRACK_MODIFICATTONS = False

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)
    nickname = db.Column(db.String(20))

db.create_all()

#user=User(username='jun',password='12345')
#db.session.add(user)
#db.session.commit()

#user=User.query.filter(User.username=='jun').first()
#user.password='123456'
#db.session.commit()
#print(user.id,user.username,user.password)

# user=User.query.filter(User.username=='jun').first()
# db.session.delete(user)
# db.session.commit()

@app.route('/')
def base():
    return render_template('base.html')

@app.route('/sign_in/',methods=['GET','POST'])
def sign_in():
    if request.method == 'GET':
        return render_template('sign_in.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 '密码错误'
        else:
            return '用户名不存在'

@app.route('/sign_up/',methods=['GET','POST'])
def sign_up():
    if request.method=='GET':
        return render_template('sign_up.html')
    else:
        usern=request.form.get('username')
        nickn= request.form.get('nickname')
        passw = request.form.get('password')
        user=User.query.filter(User.username==usern).first()
        if user:
            return '该用户名已存在'
        else:
            user1=User(username=usern,nickname=nickn,password=passw)
            db.session.add(user1)
            db.session.commit()
            return redirect(url_for('sign_in'))


@app.route('/questions/')
def questions():
    return render_template('questions.html')


if __name__ == '__main__':
    app.run()