Problem overriding sys.excepthook

[Lunchtimemama]

Yo all, I'm getting into Python for the first time and I'm really
having a blast. I've hit a bit of a snag and was wondering if someone
could lend some insight. Here be the code:

import sys
def myexcepthook(type, value, tb):
  import traceback
  rawreport = traceback.format_exception(type, value, tb)
  report = '\n'.join(rawreport)
  errorlog = open('error.log','a')
  errorlog.write(('%s\n' + '-'*30 + '\n\n') % report)
  errorlog.close()
sys.excepthook = myexcepthook

Now here's the trouble: if I enter that line-by-line into the
interpreter in interactive mode, the custom exception hook will handle
all exceptions, but if I put that in a script that I run from the
shell, it only catches some exceptions. For example, it would catch an
undefined name, like if I just put:

spam

into the program above, the override would work. But if I made a
syntactical error, like:

1 = spam

then it would fall to the standard sys.excepthook. Is there some lazy
evaluation that I don't know about? I'm on Windows, if that makes a
difference. Thank for the help.

-LTM