paul j3 added the comment: chris.jerdonek wrote: "Also, to answer a previous question, the three places in which the choices string is used are: in the usage string (separator=','), in the help string when expanding "%(choices)s" (separator=', '), and in the error message text (separator=', ' with repr() instead of str())."
In the usage string, the ',' is used to make a compact representation of the choices. The ', ' separator is used in the help line, where space isn't as tight. This 'choices formatting' is called during 'add_argument()' simply as a side effect of checking for valid parameters, especially 'nargs' (that it, is an integer or an acceptable string). Previously 'nargs' errors were not caught until 'parse_args' was used. This is discussed in http://bugs.python.org/issue9849 Argparse needs better error handling for nargs http://bugs.python.org/issue16970 argparse: bad nargs value raises misleading message On the issue of what error type to raise, my understanding is that 'ArgumentError' is the preferred choice when it affects a particular argument. parse_args() nearly always raises an ArgumentError. Once add_argument has created an action, it too can raise an ArgumentError. ArgumentError provides a standard way of identifying which action is giving the problem. While testing 'metavar="range(0,20)"', I discovered that the usage formatter strips off parenthesis. A regex expression that removes excess 'mutually exclusive group' notation is responsible for this. The simple fix is to modify the regex so it distinguishes between ' (...)' and 'range(...)'. I intend to create a new issue for this, since it affects any metavar the includes (). ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue16468> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
