paul j3 added the comment:
An alternative to Jason's example:
parser = argparse.ArgumentParser()
parser.add_argument('app')
parser.add_argument('--config')
parser.add_argument('app_args', nargs=argparse.REMAINDER)
args = parser.parse_args(['--config', 'bar', 'app'])
print vars(args)
# as expected: {'app': 'app', 'app_args': [], 'config': 'bar'}
When you have several positionals, one or more of which may have 0 arguments
(*,?,...), it is best to put all of the optional arguments first.
With 'app --config bar', parse_args identifies a 'AOA' pattern (argument,
optional, argument). It then checks which positional arguments match. 'app'
claims 1, 'app_args' claims 2 (REMAINDER means match everything that follows).
That leaves nothing for '--config'.
What you expected was that 'app' would match with the 1st string, '--config'
would match the next 2, leaving nothing for 'app_args'.
In http://bugs.python.org/issue14191 I wrote a patch that would give the
results you want if 'app_args' uses '*'. That is makes it possible to
interleave positional and optional argument strings. But it does not change
the behavior of REMAINDER.
parser.add_argument('app_args', nargs='*')
--------------
Maybe the documentation example for REMAINDER needs to modified to show just
how 'greedy' REMAINDER is. Adding a:
parser.add_argument('--arg1',action='store_true')
does not change the outcome. REMAINDER still grabs '--arg1' even though it is
a defined argument.
Namespace(arg1=False, args=['--arg1', 'XX', 'ZZ'], command='cmd', foo='B')
----------
nosy: +paul.j3
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue14174>
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