[ python-Bugs-1000439 ] optparse error method doesn't print option info

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Bugs item #1000439, was opened at 2004-07-29 21:05
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Category: Python Library
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Ivan Nestlerode (nestler)
Assigned to: Nobody/Anonymous (nobody)
Summary: optparse error method doesn't print option info

Initial Comment:
When there is an error in optparse.OptionParser's
parse_args() method, (like if the user types an
argument to an option that doesn't take one), a terse
one-line error message is printed and the program exits.

I think it would be significantly more useful if the
option documentation were printed out too, but I have
no way to make this happen currently (since exit is
called).

Please expose a toggle to print out the option info
(that stuff that is printed with -h) when there is a
parsing error. It could probably be implemented as a
Boolean argument to the OptionParser constructor.

To illustrate what I'm talking about, consider a
program called mktoc that uses the optparse module for
its parsing. Here are two runs of it.

# This prints out the one-liner usage string and the
options details
$ mktoc -h
usage: mktoc [options] [showdirectoryname]

options:
  --version             show program's version number
and exit
  -h, --help            show this help message and exit
  -a, --auto            run automatically
  -bBAND, --band=BAND   specify the band manually
  -c, --cdrdao          output cdrdao TOC format (the
default)
  -d, --data            make a data disc instead of an
audio disc
  -k, --k3b             output K3B project format

# This only prints out the one-liner usage string which
is basically
# useless without the option details. This is what
comes out of the
# error() method of the parser object.
$ mktoc --cdrdao=foo
usage: mktoc [options] [showdirectoryname]

mktoc: error: --cdrdao option does not take a value

If it isn't clear, the reason I think the option info
should be printed is for usability (if the user is
confused enough to put arguments where they don't
belong or some such thing, they probably need the more
verbose message).

Thanks,
-Ivan



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