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Re: Why is the argparse module so inflexible?

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On 05:28 Sat 29 Jun     , Steven D'Aprano wrote:
> On Fri, 28 Jun 2013 18:36:37 -0700, Ethan Furman wrote:
> 
> > On 06/27/2013 03:49 PM, Steven D'Aprano wrote:
> >>
> >> [rant]
> >> I think it is lousy design for a framework like argparse to raise a
> >> custom ArgumentError in one part of the code, only to catch it
> >> elsewhere and call sys.exit. At the very least, that OUGHT TO BE A
> >> CONFIG OPTION, and OFF BY DEFAULT.
> 
> [emphasis added]
> 
> >> Libraries should not call sys.exit, or raise SystemExit. Whether to
> >> quit or not is not the library's decision to make, that decision
> >> belongs to the application layer. Yes, the application could always
> >> catch SystemExit, but it shouldn't have to.
> > 
> > So a library that is explicitly designed to make command-line scripts
> > easier and friendlier should quit with a traceback?
> > 
> > Really?
> 
> Yes, really.
> 
> Tracebacks are not that unfriendly, generally speaking. In my experience, 
> the average non-technical person is no more confused and distressed by a 
> traceback extending over thirty lines than they are by a one line error 
> message. As the developer, I should see the tracebacks by default[1]. If 
> I want to suppress or simplify them, then I should take explicit steps to 
> do so, either by catching the exception and calling sys.exit myself, or 
> at least by setting a runtime config option to the library.
> 
> This also allows me to enable debugging in my app by showing tracebacks, 
> or disable it by hiding them. That should be my decision, not the 
> library. If the library catches exceptions then exits, throwing away 
> potentially useful information, that makes it difficult to debug anything 
> relying on the library.
> 
> I'm willing to concede that, just maybe, something like argparse could 
> default to "catch exceptions and exit" ON rather than OFF. 
> 
> 
> [1] There's something in the Zen of Python about that...
> 
> 
> -- 
> Steven
> -- 
>

Although I got confused at the first time I was using argparse (or
optparse which is now obsolte and also has this feature), I see the
value when you write scripts.  It is mostly annoying when playing with
it in a console, but there is a very easy (but partial) fix for that:
just subclass argparse.ArgumentParser:

import sys
class ArgumentParser(argparse.ArgumentParser):
    def  exit(self, status=0, message=None):
        if message:
            self._print_message(message, sys.stderr)

now the parser will not exit, though there is no ease fix to get the
traceback: self.exit() is called in various places sometimes inside
a try block.

Best regards,
Marcin http://mail.python.org/mailman/listinfo/python-list

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Why is the argparse module so inflexible? Andrew Berg <robotsondrugs@gmail.com> - 2013-06-27 07:54 -0500
  Re: Why is the argparse module so inflexible? Roy Smith <roy@panix.com> - 2013-06-27 09:08 -0400
    Re: Why is the argparse module so inflexible? Andrew Berg <robotsondrugs@gmail.com> - 2013-06-27 08:49 -0500
    Re: Why is the argparse module so inflexible? Dave Angel <davea@davea.name> - 2013-06-27 12:02 -0400
      Re: Why is the argparse module so inflexible? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-27 22:49 +0000
        Re: Why is the argparse module so inflexible? Cameron Simpson <cs@zip.com.au> - 2013-06-28 09:34 +1000
        Re: Why is the argparse module so inflexible? Ethan Furman <ethan@stoneleaf.us> - 2013-06-28 18:36 -0700
          Re: Why is the argparse module so inflexible? rusi <rustompmody@gmail.com> - 2013-06-28 21:12 -0700
            Re: Why is the argparse module so inflexible? Terry Reedy <tjreedy@udel.edu> - 2013-06-29 00:37 -0400
              Re: Why is the argparse module so inflexible? Roy Smith <roy@panix.com> - 2013-06-29 10:12 -0400
                Re: Why is the argparse module so inflexible? Andrew Berg <robotsondrugs@gmail.com> - 2013-06-29 09:17 -0500
          Re: Why is the argparse module so inflexible? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-29 05:28 +0000
            Re: Why is the argparse module so inflexible? Marcin Szamotulski <mszamot@gmail.com> - 2013-06-29 13:38 +0100
            Re: Why is the argparse module so inflexible? MRAB <python@mrabarnett.plus.com> - 2013-06-29 16:58 +0100
            Re: Why is the argparse module so inflexible? Ethan Furman <ethan@stoneleaf.us> - 2013-06-29 12:17 -0700
        Re: Why is the argparse module so inflexible? Modulok <modulok@gmail.com> - 2013-06-28 19:39 -0600
        Re: Why is the argparse module so inflexible? Isaac To <isaac.to@gmail.com> - 2013-06-29 12:37 +0800
    Re: Why is the argparse module so inflexible? Robert Kern <robert.kern@gmail.com> - 2013-06-27 20:47 +0100

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