There are may things that are hidden on the google docs.
1. Request handler for routing.

in the

class HomeHandler(webapp2.RequestHandler):
def get(self):
self.response.write('This is the HomeHandler.')

class ProductListHandler(webapp2.RequestHandler):
def get(self):
self.response.write('This is the ProductListHandler.')

class ProductHandler(webapp2.RequestHandler):
def get(self, product_id):
self.response.write('This is the ProductHandler. '
'The product id is %s' % product_id)

app = webapp2.WSGIApplication([
(r'/', HomeHandler),
(r'/products', ProductListHandler),
(r'/products/(\d+)', ProductHandler), 

Here is the link to this and more
about the routing. man
http://webapp-improved.appspot.com/guide/routing.html#simple-routes link
There are more
This is about the domain routing.>>>>

import webapp2
from webapp2_extras import routes

app = webapp2.WSGIApplication([
routes.DomainRoute('<subdomain>.app-id.appspot.com', [
webapp2.Route('/', handler=SubdomainHomeHandler, name='subdomain-home'),
webapp2.Route('/', handler=HomeHandler, name='home'),

  ===== to get the url and query_arguments
Try this:
Also, if you just need the querystring, this will work:
And, lastly, if you know the querystring variable that you're looking for, you can do this:
or use can use this 
    query_sting = self.request.GET

And more to learn here.