paul j3 added the comment:
http://stackoverflow.com/questions/25626109/python-argparse-conditionally-required-arguments
asks about implementing a 'conditionally-required-arguments' case in
`argparse`. The post-parsing test is simple enough:
if args.argument and (args.a is None or args.b is None):
# raise argparse error here
I believe the clearest and shortest expression using Groups is:
p = ArgumentParser(formatter_class=UsageGroupHelpFormatter)
g1 = p.add_usage_group(kind='nand', dest='nand1')
g1.add_argument('--arg', metavar='C')
g11 = g1.add_usage_group(kind='nand', dest='nand2')
g11.add_argument('-a')
g11.add_argument('-b')
The usage is (using !() to mark a 'nand' test):
usage: issue25626109.py [-h] !(--arg C & !(-a A & -b B))
This uses a 'nand' group, with a 'not-all' test (False if all its actions are
present, True otherwise).
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