As far as I know, every request has around 10-second runtime limitation. You may have seen this in your log:

<class 'google.appengine.runtime.DeadlineExceededError'>:
Traceback (most recent call last):
  File "/base/data/home/apps/brps/1.330485825438182004/index.py", line 149, in <module>
    main()
  File "/base/data/home/apps/brps/1.330485825438182004/index.py", line 145, in main
    run_wsgi_app(application)
  File "/base/python_lib/versions/1/google/appengine/ext/webapp/util.py", line 76, in run_wsgi_app
    result = application(env, _start_response)
[snip]

For sake of user experience, we need to deal with that. This post explains where you can import DeadlineExceededError.

# DeadlineExceededError can live in two different places
try:
  # When deployed
  from google.appengine.runtime import DeadlineExceededError
except ImportError:
  # In the development server
  from google.appengine.runtime.apiproxy_errors import DeadlineExceededError

By throwing in my app, the time is around 8.5 seconds. If you try to catch it, it does work, but what if you try to stall? (Yeah, you are a bad boy!)

class DeadlineExceededErrorPage(webapp.RequestHandler):
  def get(self):
    try:
      time.sleep(20)
      logging.debug('Impossible!')
    except DeadlineExceededError:
      logging.debug('Houston, we got a problem! But we are going to make it worse!')
      time.sleep(20)
      logging.debug('Houston, we really are in a big trouble!')
    logging.debug('We should never be here!')
    self.response.out.write('Done!')

I made this piece of code to try on production server (It didnt run as my expectation on development server, maybe I need to use urlfetch instead of sleep?), here is the log:

1.01-05 05:55AM 23.941 /DeadlineExceededError 500 9151ms 139ms-cpu 0kb
  118.169.142.109 - - [05/Jan/2009:05:55:33 -0800] "GET /DeadlineExceededError HTTP/1.1" 500 0 - -

2.D 01-05 05:55AM 32.687
  Houston, we got a problem! But we are going to make it worse!

3.E 01-05 05:55AM 33.090
  <class 'google.appengine.runtime.DeadlineExceededError'>:
  Traceback (most recent call last):
    File "/base/data/home/apps/yjltest/1.330487966959697473/index.py", line 55, in main
      run_wsgi_app(application)
    File "/base/python_lib/versions/1/google/appengine/ext/webapp/util.py", line 76, in run_wsgi_app
      result = application(env, _start_response)
    File "/base/python_lib/versions/1/google/appengine/ext/webapp/__init__.py", line 498, in __call__
      handler.get(*groups)
    File "/base/data/home/apps/yjltest/1.330487966959697473/index.py", line 41, in get
      time.sleep(20)

Time to catch the exception is about 8.7 seconds, then at 9.1 seconds, we know the answer of the stalling, that is getting another DeadlineExceededError.

If you are really bad, you would ask why not try again? I tried, we dont have the second chance!