paul j3 added the comment:
Try `nargs='?'` or try providing a `default` along with the '*'.
Including your ARGUMENT action in the error message is intentional.
The test for this error message is:
required_actions = []
for action in self._actions:
if action not in seen_actions:
if action.required:
Originally the code just checked if `positionals` was empty. That was the list
of positional Actions. Actions were popped as they were parsed. Now it
maintains a set `seen_actions`, and checks the `required` attribute. This test
applies to both positionals and optionals.
For optionals, `required` is set by the programmer. But for positionals it is
set with:
def _get_positional_kwargs
...
# mark positional arguments as required if at least one is
# always required
if kwargs.get('nargs') not in [OPTIONAL, ZERO_OR_MORE]:
kwargs['required'] = True
if kwargs.get('nargs') == ZERO_OR_MORE and 'default' not in kwargs:
kwargs['required'] = True
So for '?' argument, required is False. But for '*', it must also have a
'default' parameter (not just the default None).
So the proposed patch is overriding the 'required' value that was set during
'add_argument'. And issuing this error message is the main purpose of the
'required' attribute.
I would not implement this patch.
But it would be a good idea to check if this method of setting the required
attribute has been discussed in other bug/issues. (There is an open issue
concerning how the 'required' is set/or not for the subparsers positional.)
Off hand I don't see anything about this in the documentation. Maybe that's
what needs to be patched. (It's easier and safer to change the documentation
than the working code. Backward compatibility is a major concern when changing
the code.)
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue28609>
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