from flask import Flask,render_template,session,request,abort, redirect, url_for
app = Flask(__name__)    创建了这个类的实例

@app.route('/', methods=['GET', 'POST'])               
def hello_world():
    return redirect(url_for('login'))   重定向到/login，url_for函数

@app.route('/login')
def login():
    abort(401)
    this_is_never_executed()

@app.errorhandler(404)
def page_not_found(error):
    return render_template('page_not_found.html'), 404   自定义404错误页面

@app.route('/user/<username>')   变量名
def show_user_profile(username):
    # show the user profile for that user
    return 'User %s' % username    传入变量

登录
@app.route('/')
def index():
    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':
        session['username'] = request.form['username']
        return redirect(url_for('index'))
    return '''
        <form action="" method="post">
            <p><input type=text name=username>
            <p><input type=submit value=Login>
        </form>
    '''

@app.route('/logout')
def logout():
    # 如果会话中有用户名就删除它。
    session.pop('username', None)
    return redirect(url_for('index'))

# 设置密钥，复杂一点：
app.secret_key = 'A0Zr98j/3yX R~XHH!jmN]LWX/,?RT'

if __name__ == '__main__':
    app.run(host='0.0.0.0',debug=True,)