new_contents: from flask import Flask
  from flask import request
  
  app = Flask(__name__)
  
  @app.route('/', methods=['GET', 'POST'])
  def home():
  	return '<h1>Home</h1>'
  	
  @app.route('/signin', methods=['GET'])
  def signin_form():
  	return '''<form action="/signin" method="post">
  	          <p><input name="username"></p>
  	          <p><input name="password" type="password"></p>
  	          <p><button type="submit">Sign In</p>
  	          </form>
  	       '''
  @app.route('/signin', methods=['POST'])
  def signin():
  	# 需要从request对象读取表单内容：
  	if request.form['username']=='admin' and request.form['password']=='password':
  		return '<h3>Hello, admin!</h3>'
  	return '<h3>Bad username or password.</h3>'
  
  if __name__ == '__main__':
  	app.run()
  	
subject: add do_flask.py