paul j3 added the comment:
Further observations:
parser.add_subparsers() accepts a 'dest' keyword arg, but not a 'required' one.
Default of 'dest' is SUPPRESS, so the name does not appear in the Namespace.
Changing it to something like 'command' will produce an entry, e.g.
Namespace(command=foo, ...). Is this a problem?
Assuming we have a clean way of assigning a name to 'subparsers', what should
it be? 'command', '{cmd}', '{foo,bar,baz}' (like in the usage line)? This
name also could be used when telling the user the subparser choice is invalid
(parser._check_value).
This issue exposes a problem with '_get_action_name()'. This function gets a
name from the action's option_strings, metavar or dest. If it can't get a
string, it returns None.
ArgumentError pays attention to whether this action name is a string or None,
and adjusts its message accordingly. But the new replacement for the 'too few
arguments' error message does a ', '.join([action names]), which chokes if one
of those names is None. There is a mutually_exclusive_groups test that also
uses this 'join'. This bug should be fixed regardless of what is done with
subparsers error messages.
So the issues are:
- making 'subparsers' a required argument
- choosing or generating an appropriate name for 'subparsers'
- passing this name to the error message (via _get_action_name?)
- correcting the handling of action names when they are unknown (None).
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue9253>
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