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

Eric Smith eric at trueblade.com
Tue Sep 29 22:56:38 CEST 2009

Paul Moore wrote:
> 2009/9/28 Yuvgoog Greenle <ubershmekel at gmail.com>:
>> 1. There is no chance of the script killing itself. In argparse and optparse
>> exit() is called on every parsing error (btw because of this it sucks to
>> debug parse_args in an interpreter).
> That one does worry me. I'd rather argparse (or any library function)
> didn't call sys.exit on my behalf - it should raise an exception. Is
> it actually true that argparse exits? (I can imagine that it might if
> --help was specified, for example. An exception may not be right here,
> but I still don't like the idea of a straight exit - I've used too
> many C libraries that think they know when I want to exit).

You can override ArgumentParser.error() to raise an exception.

>> 2. There is no chance the parser will print things I don't want it to print.
> That may also be bad - for example, Windows GUI-mode programs raise an
> error if they write to stdout/stderr. I could imagine using argparse
> for such a program, and wanting to do something with --help other than
> write to stdout and exit (a message box, for example). And yet, I'd
> want access to the text argparse would otherwise write to stdout.

It looks like this might not be so easy to do. I'd suggest adding a 
file-like object to the constructor, defaulting to sys.stderr; or maybe 
an ArgumentParser.print() method that can be overridden.


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