Peter Otten <__pete...@web.de> [2015-11-06 11:57 +0100]:
For example, with the above code my_prog -v hello world works well, but my_prog -v -x hello world Fails with an error message 'error: unrecognized arguments: -x'.This looks like a bug to me. Please report it on bug.python.org.
Why does it looks like a bug? To me it seems okay - argparse expects that an argument that starts with '-' is an option, and it also expects to be told about all possible options, so it complains on encountering an unrecognized 'option'. This is why a special delimiter is needed to mark the 'end of options'.
If I invoke the program with a '--' at the end of the options (as I understand is a common standard and a POSIX recommendation), as in: my_prog -v -- -x hello world It works well again. However, a few questions remain: Firstly, as far as I can tell the use of '--' is not documented in the argparse documentation (but the code of argparse clearly shows that it is a feature). Secondly, when using '--', this string itself is inserted into the list of the collected positional arguments (in the above example in the cmd_args variable): $ ./my_prog -v -- -x hello world Namespace(cmd_args=['--', '-x', 'hello', 'world'], verbose=True) It's quiet easy to check for it and remove it if it exists, but it still seems like it shouldn't be there - it is not really an argument, just a delimiter.I'm not sure about this one; one purpose of REMAINDER is to pass on the unprocessed arguments to another program/script, and this might follow the same convention. Should parser.add_argument('-v', '--verbose', action='store_true') parser.add_argument('cmd_args', nargs=argparse.REMAINDER) args = parser.parse_args() subprocess.call(["rm"] + args.cmd_args) $ my_prog -v -- -r foo attempt to delete two files "-r" and "foo" or remove the "foo" directory? The first is the safer alternative, and as you say stripping the "--" is easy.
I'm using the REMAINDER exactly for passing on arguments to another program, as in your example. I would expect that everything after the '--' should be passed on as is - it should be up to the other program to decide what to do with the arguments it receives (So in your examples, rm would actually try to remove the "foo" directory). And although stripping the '--' is easy, why should the user of argparse need to handle it? Still unclear to me. Cheers, Amit -- https://mail.python.org/mailman/listinfo/python-list
