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。

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

主python文件：

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)
    telephone = db.Column(db.String(11), nullable=False)

# db.create_all()

# 增加数据
# user=User(username = 'mis1234',password = '111111',telephone = '12345678900')
# db.session.add(user)
# db.session.commit()

# 查询数据

# user=User.query.filter(user.username == 'mis1234').first()
# print(user.username,user.password)

# 修改数据
# user=User.query.filter(user.username == 'mis1234').first()
# user.password = '000000'
# db.session.commit()

# 删除数据
# user=User.query.filter(user.username == 'mis1234').first()
# db.session.delete(user)
# db.session.commit()

@app.route('/login/', methods=['GET', 'POST'])
def login():
    if request.method == 'GET':
        return render_template('login.html')
    else:
        usern = request.form.get('username')
        passw = request.form.get('password')
        user = User.query.filter(User.username == usern).first()
        if user:
            if user.password == passw:
                session['user'] = usern
                return redirect(url_for('index'))
            else:
                return 'password error.'
        else:
             return 'username is not existed.'

@app.route('/register/', methods=['GET', 'POST'])
def register():
    if request.method == 'GET':
        return render_template('register.html')
    else:
        usern = request.form.get('username')
        telep = request.form.get('telephone')
        passw = request.form.get('password')
        user = User.query.filter(User.username == usern).first()
        if user:
            return 'username existed.'
        else:
            user1 = User(username=usern, password=passw, telephone=telep)
            db.session.add(user1)  # 数据库操作
            db.session.commit()
            return redirect(url_for('login'))

@app.route('/question', methods=['GET', 'POST'])
def question():
    return render_template('question.html')

@app.route('/base', methods=['GET', 'POST'])
def base():
    return render_template('base.html')

@app.route('/', methods=['GET', 'POST'])
def index():
    return render_template('index.html')

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

config.python:

#encoding:utf-8
import os
DEBUG = True
SECRET_KEY = os.urandom(24)
SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:@127.0.0.1:3306/mis_db?charset=utf8'
SQLALCHEMY_TRACK_MODIFICATIONS = False