完成登录功能，用session记住用户名

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=TabError,autoincrement=True)
    username=db.Column(db.String(20),nullable=False)
    password=db.Column(db.String(20),nullable=False)
    nickname = db.Column(db.String(20), nullable=True)
# db.create_all()    #是否链接成功
 
 
# 数据添加
# user=User(username='ma',password='gg')
# db.session.add(user)
# db.session.commit()
#
#
# 数据更新
#
# user = User.query.filter(User.username=='hh').first()
# user.password='gg'
# db.session.commit()
#
#
# 数据查询
# user = User.query.filter(User.username=='ma').first()
# print(user.username,user.password)
#
# 数据删除
# user = User.query.filter(User.username=='ma').first()
# db.session.delete(user)
# db.session.commit()
 
 
# session会话连接
# filter()过滤器
# route制定路径和函数之间的关系
# def定义一个变量
 
@app.route('/')
def switch():
    return render_template('switch.html')
 
 
@app.route('/login/',methods=['GET','POST'])# 跳转登陆,methods定义它有两种请求方式
def login():
    if request.method == 'GET':
      return render_template('login.html')
    else:
        username = request.form.get('user')
        password = request.form.get('psw')
        user = User.query.filter(User.username == username).first()  # 判断用户名是否存在
        if user:
            if user.password==password:
                session['username'] = username
                session.permanent = True
                return   redirect(url_for('switch'))
            else:
                return u'密码错误'
        else:
            return u'用户名不存在'
 
 
@app.route('/register/',methods=['GET','POST'])# 跳转注册,methods定义它有两种请求方式
def register():
    if request.method == 'GET':
        return render_template('register.html')
    else:
 
        username = request.form.get('user')
        password = request.form.get('psw')
        nickname = request.form.get('nickname')
        user = User.query.filter(User.username == username).first() # 判断用户名是否存在
        if user:
            return u'该用户已存在'
        else:
            user = User(username=username,password=password,nickname=nickname)
            db.session.add(user)
            db.session.commit()
            return redirect(url_for('login'))
 
@app.route('/wenda/')
def wenda():
    return render_template('wenda.html')
 
 
 
if __name__ == '__main__':
    app.run(debug=True)