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To: python-list@python.org
From: rh <richard_hubbe11@lavabit.com>
Subject: Re: How does one make argparse print usage when no options are provided on the command line?
Date: Thu, 6 Dec 2012 10:42:19 -0800
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On Thu, 06 Dec 2012 00:06:29 -0500
Terry Reedy <tjreedy@udel.edu> wrote:

> On 12/5/2012 7:48 PM, rh wrote:
> > On Wed, 5 Dec 2012 18:42:37 +0100
> > Bruno Dupuis <python.ml.bruno.dupuis@lisael.org> wrote:
> >
> >> On Wed, Dec 05, 2012 at 08:48:30AM -0800, rh wrote:
> >>> I have argparse working with one exception. I wanted the program
> >>> to print out usage when no command line options are given. But I
> >>> only came across other examples where people didn't use argparse
> >>> but instead printed out a separate usage statement. So they used
> >>> argparse for everything but the case where no command line args
> >>> are given.
> >>>
> >>
> >> this is quite raw, but i'd add
> >>
> >> import sys
> >> if len(sys.argv) == 1:
> >>      sys.argv.append('-h')
> >
> > This works too. I guess I like the print_usage() method better.
> >
> > Being new to python I have noticed that I had copied a bit of code
> > that did
> >
> > if len(sys.argv[1:]) == 0:
> 
> This needlessly creates and tosses a new object.
> >
> > You did this:
> > if len(sys.argv) == 1:
> 
> This does not.
> 
> > The other reply did this:
> > if len(sys.argv) <= 1:
> 
> This allows for the possibility that len(sys.argv) == 0. However,
> that can (according to the doc) only happen when starting the
> interpreter interactively without a script. Since that does not apply
> to code within a .py file, I prefer == 1.
> 
> "argv[0] is the script name (it is operating system dependent whether 
> this is a full pathname or not). If the command was executed using
> the -c command line option to the interpreter, argv[0] is set to the
> string '-c'. If no script name was passed to the Python interpreter,
> argv[0] is the empty string."

Interesting, I thought maybe <= 1 was to handle some strange case
where sys.argv < 0.  And I guess I stick with  == 1. Always good to know
from the get go what's the best way to do the basics.

> 
> -- 
> Terry Jan Reedy
> 


--