On Mon, Jan 27, 2014 at 12:02 AM, me <no...@all.net> wrote:
> On Mon, 27 Jan 2014 00:36:20 -0500, Dave Angel wrote:
>
>> sys.exit() raises an exception, and you're deliberately eating
>> that exception.
>>
>
> I can buy that sys.exit (may) be throwing an exception...My point of
> contention isn't that I may be throwing one, but why would a subsequent
> "raise" in the except: clause cause the point of program execution to
> jump back up to the sys.exit(0) and then function correctly.
You've missed the point here. sys.exit() *does* raise an exception:
SystemExit, a subclass of BaseException. In fact, you can implement
sys.exit in pure Python like so:
def exit(status):
raise SystemExit(status)
Your bare 'except:' catches that SystemExit along with any other
possible exception; the bare 'raise' in the except clause just
re-raises the same SystemExit, which then does what you meant for it
to do in the first place.
Exception classes form a hierarchy, with BaseException being the base
(obviously :)), "except:" is really just shorthand for "except
BaseException:", and is very rarely a good idea. Deriving from
BaseException are SystemExit, KeyboardInterrupt, and Exception.
SystemExit is the exception raised by sys.exit(), which if left
unhandled, the interpreter takes as a sign to shut down gracefully.
KeyboardInterrupt is raised by Ctrl+C, or (more accurately, if I'm not
mistaken) by sending SIGINT to the process. Exception is the base
class for all other exceptions, such as TypeError, ValueError,
OSError, etc., and is what you actually want to catch if you really
don't care what exception is raised but want to handle it (though in
most cases, you either should care, or should at least report what the
exception was, preferably with a traceback...which is easiest to do by
not trying to catch the exception at all).
I would suggest skimming through the Python tutorial and/or language
reference if you haven't before, there's a lot of good information in
there that will make your life with Python much easier.
And, please take this positively, but from your posted code it's
fairly apparent that Python is not your native tongue :). For
instance, you don't need the backslashes in your defaultparams
assignment; the parser knows it needs to keep looking on subsequent
lines when it hasn't found the closing '}' yet. Also, you can iterate
over a (sys.argv) in a for loop, replacing 'l', 'idx', and the while
loop; something like
for arg in a:
if arg == '-h':
print help # help being defined elsewhere...
elif arg == '-hh':
# no really, print help
print 'help'
And the big one, argument parsing is a solved problem in Python.
Check out the argparse module in the standard library (or if you're
using an older version of Python, try either optparse or getopt. It's
really a thrice-solved problem ;)).
I hope I've been of some help,
--
Zach
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