Issue 14046: argparse: assertion failure if optional argument has square/round brackets in metavar (original) (raw)

I have a web server written in python which takes an optional argument telling it what IP and port to bind to. Here's the definition:

parser.add_argument( '-b', '--bind', metavar="[ip]:port", type=unicode, help="IP and port to bind to." )

There are several other arguments as well. When the usage is printed (due to parse failures or -h), if the command line is longer than terminal width, it is wrapped. Here is the (relevant) code in argparse.py:311 which deals with this scenario:

wrap the usage parts if it's too long

text_width = self._width - self._current_indent if len(prefix) + len(usage) > text_width:

break usage into wrappable parts

part_regexp = r'(.?)+|[.?]+|\S+' opt_usage = format(optionals, groups) pos_usage = format(positionals, groups) opt_parts = _re.findall(part_regexp, opt_usage) pos_parts = _re.findall(part_regexp, pos_usage) assert ' '.join(opt_parts) == opt_usage assert ' '.join(pos_parts) == pos_usage

Note how part_regexp extracts words, and text surrounded with round/square brackets. Now the argument I defined above, when displayed in usage text, looks like this: [-b [ip]:port]

part_regexp however, will cut it into "[-b [ip]" and ":port]" and concatenated later with " ", it will have an extra space which causes the first assertion to fail.

I fiddled with part_regexp but that proved unreliable at best. I think the opt_parts should be obtained, not from the final formatted text, but from actual argument objects.

For a demonstration, see the attachment.