Clean Exception Tracking, Beautiful Code

I really wanted a way to track my exceptions without making my code look ugly. The answer seemed to be to use Python's decorators in some way, but they introduce a twist... decorators return functions, so checking the exception information always yields an exception inside a decorator.

As an example, see the following:

import inspect
def test_handler(func):
   def func2(*args, **kwargs):
       try:
           return func(*args, **kwargs)
       except Exception, e:
           print "excepted"
           (file,line,fname,context,ind) =
                 inspect.getframeinfo(inspect.currentframe())
           print "Func: %s" % (str(fname))
   return func2

@test_handler
def run_user_codes():
   k = {}
   k['test']

if __name__ == "__main__":
   print "In main"
   try:
       run_user_codes()
   except Exception, e:
       str(e)

When you run that, the output will be:

In main
excepted
Func: func2

To solve this problem, you can use the traceback module to get accurate data regarding the actual exception. For example:

import sys, traceback

class TrackException(Exception):
   def __init__(self, tb=None):
       self._tb = []
       self._tb.append(tb)
      
   def add_tb(self, tb):
       self._tb.append(tb)
      
   def __str__(self):
       string = ""
       count = 0
       for t in self._tb:
           (file, line, funcname, codestr) = t
           string += "[%d] %s (line %d, in %s): %s\n" %
                      (count,file, line, funcname, codestr)
           count += 1
       return string
  
   def __getitem__(self, y):
       return self._tb[y]
      
def inspected_exception_handler(func):
   def func2(*args, **kwargs):
       try:
           return func(*args, **kwargs)
       except TrackException, e:
           (t,v,tb) = sys.exc_info()
           list = traceback.extract_tb(tb)
           e.add_tb(list[1])
           raise e
       except Exception, e:
           (t,v,tb) = sys.exc_info()
           list = traceback.extract_tb(tb)
           raise TrackException(list[1])
   return func2


@inspected_exception_handler
def run_user_code():
   k = {}
   k['test']
  
@inspected_exception_handler   
def func():
   run_user_code()

if __name__ == "__main__":
   try:
       func()
   except Exception, e:
       print str(e)

Including the above code in your code makes tracking function exceptions much easier without cluttering your code.