HTML in Google App Engine -

i have been following this example google's site, having trouble understanding of how underlying things work. mostly, when submit text, in mainhandler html, how know use guestbook? assume has <form action="/sign" method=post> , ('/sign', guestbook) i'm not entirely sure how works.

from google.appengine.ext import db import webapp2  class greeting(db.model):     content = db.stringproperty(multiline=true)     date = db.datetimeproperty(auto_now_add=true)  class mainhandler(webapp2.requesthandler):     def get(self):         self.response.write('hello world!')         self.response.write('<h1>my guestbook</h1><ol>')         #greetings = db.gqlquery("select * greeting")         greetings = greeting.all()         greeting in greetings:             self.response.write('<li> %s' % greeting.content)         self.response.write('''             </ol><hr>             <form action="/sign" method=post>             <textarea name=content rows=3 cols=60></textarea>             <br><input type=submit value="sign guestbook">             </form>         ''')  class guestbook(webapp2.requesthandler):     def post(self):         greeting = greeting()         greeting.content = self.request.get('content')         greeting.put()         self.redirect('/')  app = webapp2.wsgiapplication([     ('/', mainhandler),     ('/sign', guestbook), ], debug=true) 

you correct! routes configured in following block:

app = webapp2.wsgiapplication([     ('/', mainhandler),     ('/sign', guestbook), ], debug=true) 

so when there request /sign, new guestbook instance created, , appropriate method called guestbook instance (which contains reference request) first argument. in example, post, webapp2 supports of popular http methods documented @ http://webapp-improved.appspot.com/guide/handlers.html