from flask import Flask, session, redirect, url_for, escape, requestapp = Flask(__name__)@app.route(‘/‘)def index():    #判断username是否存在session中    if ‘username‘ in session:        return ‘Logged in as %s‘ % escape(session[‘username‘])    return ‘You are not logged in‘@app.route(‘/login‘, methods=[‘GET‘, ‘POST‘])def login():    if request.method == ‘POST‘:        #设置session username为输入的表单值        session[‘username‘] = request.form[‘username‘]        #重定向到首页        return redirect(url_for(‘index‘))    return ‘‘‘        <form action="" method="post">            <p><input type=text name=username>            <p><input type=submit value=http://www.mamicode.com/Login>>‘‘‘@app.route(‘/logout‘)def logout():    # 移除一个username session    session.pop(‘username‘, None)    return redirect(url_for(‘index‘))#设置一个安全keyapp.secret_key = ‘A0Zr98j/3yX R~XHH!jmN]LWX/,?RT‘app.run()