Change -x and -y options to have their argument optional

[UffeJakobsen]

Options -x and -y becomes reporting options - When no NS argument is supplied

[UffeJakobsen]

Did you have a chance to look at this pull ? :-)

[dlenski]

Thanks for the reminder. I like the idea, but the problem is that nargs='?' is extremely unintuitive in its actual behavior.

#!/usr/bin/env python3

import argparse
p = argparse.ArgumentParser()
p.add_argument('filenames', nargs='*')
p.add_argument('--test', nargs='?')
p.add_argument('--other', action='store_true')

args1 = p.parse_args(['foo','bar','--test'])
print(args1)

args2 = p.parse_args(['--test=testARG','foobar'])
print(args2)

args3 = p.parse_args(['--test','testARG','foobar'])
print(args3)

args4 = p.parse_args(['--test','--other'])
print(args4)

args5 = p.parse_args(['--test','will_this_be_the_argument_of_test_or_a_filename?','--other'])
print(args5)

Output:

Namespace(filenames=['foo', 'bar'], other=False, test=None)
Namespace(filenames=['foobar'], other=False, test='testARG')
Namespace(filenames=['foobar'], other=False, test='testARG')
Namespace(filenames=[], other=True, test=None)
Namespace(filenames=[], other=True, test='will_this_be_the_argument_of_test_or_a_filename?')

In other words, an option with nargs='?' does not provide a reasonably mechanism to signal that whatever follows that option on the command-line argument is not intended as the argument of that option.

Because of this extremely unintuitive behavior, and because there is no better way to create an "argument-optional" option using the Python standard library… I don't want to use nargs='?' within wtf. 🤷‍♂️

[dlenski]

If you can think of a simple way to implement "argument-optional" options that doesn't exhibit the surprising behavior of the args5 case above, and doesn't use anything outside the standard library… I'm definitely open to it. :-)

[UffeJakobsen]

@dlenski: Thanks for your reply :-)

I understand your concern about nargs='?'...

Changing the input files from nargs='*' into nargs=argparse.REMAINDER will solve parts of the problem by forcing the files into always appearing as the last elements on the cmd line - but it will just open new problems....
The nargs=argparse.REMAINDER is handled somewhat strange inside argparse (default does not work for it - and the '--' separator between options and arguments is not handled by argparse anymore)

Another more logical approach - would be introducing -X and -Y as options that only does reporting and no changes compared to their lower-case equivalents.
That approach is in line with your current semantics (upper-case options are reporting options - lower-case options changes output)

Only problem with that is that the -X option is already used to exit without any errorcode

Question is if you would accept changing the existing -X option to another one ?

[dlenski]

Another more logical approach - would be introducing -X and -Y as options that only does reporting and no changes compared to their lower-case equivalents.
That approach is in line with your current semantics (upper-case options are reporting options - lower-case options changes output)

Only problem with that is that the -X option is already used to exit without any errorcode

Question is if you would accept changing the existing -X option to another one ?

Yeah, this seems like the most reasonable approach. Good ideas. How about change the existing -X to… hrm, -N?

[UffeJakobsen]

Great - I'll rework the pull request :-)