How to limit python traceback to specific files

I write a lot of Python code that uses external libraries. Frequently I will write a bug, and when I run the code I get a big long traceback in the Python console. 99.999999% of the time it's due to a coding error in my code, not because of a bug in the package. But the traceback goes all the way to the line of error in the package code, and either it takes a lot of scrolling through the traceback to find the code I wrote, or the traceback is so deep into the package that my own code doesn't even appear in the traceback.

Is there a way to "black-box" the package code, or somehow only show traceback lines from my code? I'd like the ability to specify to the system which directories or files I want to see traceback from.

Solution

In order to print your own stacktrace, you would need to handle all unhandled exceptions yourself; this is how the sys.excepthook becomes handy.

The signature for this function is sys.excepthook(type, value, traceback) and its job is:

This function prints out a given traceback and exception to sys.stderr.

So as long as you can play with the traceback and only extract the portion you care about you should be fine. Testing frameworks do that very frequently; they have custom assert functions which usually does not appear in the traceback, in other words they skip the frames that belong to the test framework. Also, in those cases, the tests usually are started by the test framework as well.

You end up with a traceback that looks like this:

[ custom assert code ] + ... [ code under test ] ... + [ test runner code ]

How to identify your code.

You can add a global to your code:

__mycode = True

Then to identify the frames:

def is_mycode(tb):
  globals = tb.tb_frame.f_globals
  return globals.has_key('__mycode')

How to extract your frames.

skip the frames that don't matter to you (e.g. custom assert code)
identify how many frames are part of your code -> length

extract length frames

def mycode_traceback_levels(tb):
  length = 0
  while tb and is_mycode(tb):
    tb = tb.tb_next
    length += 1
  return length

Example handler.

def handle_exception(type, value, tb):
  # 1. skip custom assert code, e.g.
  # while tb and is_custom_assert_code(tb):
  #   tb = tb.tb_next
  # 2. only display your code
  length = mycode_traceback_levels(tb)
  print ''.join(traceback.format_exception(type, value, tb, length))

install the handler:

sys.excepthook = handle_exception

What next?

You could adjust length to add one or more levels if you still want some info about where the failure is outside of your own code.