Every so often I'm confronted with being unable to determine where an
exception is being raised. Unfortunately pdb (Python debugger) cannot be
set to break on an exception (oddly missing functionality).
It turns out that pdb is built upon a simple Python API, a callback that
is invoked whenever the interpreter "steps". The callback is set with
sys.settrace() (see Python doc for full explanation).
To find my elusive exception I simply added this tiny bit of code that
sets the tracing function and whenever a TypeError occurred it printed
out the stacktrace.
Caveat, it's verbose, will print out every TypeError exception including
those you're not looking for and it will do so for every place on the
stack. A somewhat minor inconvenience if you can't find the exception
using any of the other means. You can of course tweak this to be much
more specific by examining the other context information passed to the
callback but for a quick dirty hack it didn't seem worthwhile.
Hope its useful to someone.
John
import sys
import traceback
def tracefunc(frame, event, arg):
if event == 'exception':
exc, value, tb = arg
if isinstance(value, TypeError):
print ">>> Exception %s" % value
print ''.join(traceback.format_tb(tb))
return tracefunc
sys.settrace(tracefunc)
--
John Dennis <jden...@redhat.com>
Looking to carve out IT costs?
www.redhat.com/carveoutcosts/
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