Better way to handle errors in tornado request handler

Question

There are two similar handlers: AgeHandler1 and AgeHandler2. In the first one we simply raise a specific exception to return an error message, in the second - we manually return

Answer 1

Overwriting write_error works very well. What I do in my projects is I try to catch any 500 status codes. I then send them to myself over slack (my traffic is low enough that the frequency is very low).

Here's the code to extract a clean stack trace from write_error. Note in this example I also yank out any references to 'gen.py', 'concurrent.py' or 'web.py', which makes for much cleaner stack traces.

import tornado.web, traceback, logging

class MyRequestHandler(tornado.web.RequestHandler):
   def write_error(self,status_code,**kwargs):
      if status_code == 500:
         excp = kwargs['exc_info'][1]
         tb   = kwargs['exc_info'][2]
         stack = traceback.extract_tb(tb)
         clean_stack = [i for i in stack if i[0][-6:] != 'gen.py' and i[0][-13:] != 'concurrent.py']
         error_msg = '{}\n  Exception: {}'.format(''.join(traceback.format_list(clean_stack)),excp)

         # do something with this error now... e.g., send it to yourself
         # on slack, or log it.
         logging.error(error_msg)  # do something with your error...

     # don't forget to show a user friendly error page!
     self.render("oops.html")  

The output looks like this:

  File "app.py", line 55, in get
    assert 1==2,"A fake error to trigger a critical alert."

  Exception: A fake error to trigger a critical alert.