traceback as string

[John Hunter]

What is the best way to get the traceback as a string.  I tried

def exception_to_str(s = None):

   sh = StringIO.StringIO()
   if s is not None: print >>sh, s
   traceback.print_stack(sh)
   return sh.getvalue()


but got

Traceback (most recent call last):
  File "/home/jdhunter/seizure/python/eegdb/eegview/eegview.py", line 944, in on_menuFileOpen_activate
    msg = exception_to_str('Could not read data:')
  File "/hunter/jdhunter/python/projects/jdh/jdh/cbook.py", line 707, in exception_to_str
    traceback.print_stack(sh)
  File "/usr/local/lib/python2.3/traceback.py", line 235, in print_stack
    print_list(extract_stack(f, limit), file)
  File "/usr/local/lib/python2.3/traceback.py", line 266, in extract_stack
    lineno = f.f_lineno

Thanks!
John Hunter