[Python-Dev] PEP 389: argparse - new command line parsing module

[André Malo]

* Steven D'Aprano wrote:

> You don't need a comment warning that you are catching SystemExit
> because parse_args raises SystemExit, any more than you need a comment
> saying that you are catching ValueError because some function raises
> ValueError. The fact that you are catching an exception implies that
> the function might raise that exception. A comment like:
>
> "Catching SystemExit because parse_args() throws SystemExit on parser
> errors."
>
> is up them with comments like this:
>
> x += 1  # Add 1 to x.

It's semantically different. You usually don't catch SystemExit directly, 
because you want your programs to be stopped. Additionally, a library 
exiting your program is badly designed, as it's unexpected. Thatswhy such a 
comment is useful.

Here's what I'd do: I'd subclass SystemExit in this case and raise the 
subclass from argparse. That way all parties here should be satisifed. (I 
do the same all the time in my signal handlers - that's another reason I'd 
rather not catch SystemExit directly as well :-)

nd
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