python 2.7-argparse：可选参数的参数

Question

I have the following Code Snippet.

parser = argparse.ArgumentParser()
parser.set_defaults(func=lambda x: parser.print_usage())

parser.add_argument('-o', '--overview', help="print overview",
                    action='store_true')

parser.add_argument('-a', '--add', help='add sudo item', nargs='*',
                    dest="ldap_attrs")
parser.add_argument('dn, object_class, attributes', nargs='*')

parser.add_argument('-d', '--delete', help='delete sudo item', dest='action',
                    action='store_const', const=deleteItem)
parsed_args = parser.parse_args()

It prints out the following:

usage: sudoadm.py [-h] [-o] [-a [LDAP_ATTRS [LDAP_ATTRS ...]]] [-d]

                  [dn, object_class, attributes [dn, object_class, attributes ...]]

positional arguments:
  dn, object_class, attributes

optional arguments:
  -h, --help            show this help message and exit
  -o, --overview        print overview
  -a [LDAP_ATTRS [LDAP_ATTRS ...]], --add [LDAP_ATTRS [LDAP_ATTRS ...]]
                        add sudo item
  -d, --delete          delete sudo item

I want the positional Arguments as Input Parametes to the -a Argument (eg: -a dn, object_class, attributes), and if possible the positional Paramters printed in the help message instead of LDAP_ATTRS ( eg: -a [dn, object_class, attributes])?

Answer 1

When defining a positional, the call is:

parser.add_argument(dest, nargs='*', help='...', ...)

That is, the one non-keyword argument is the dest , the name of the attribute in args . That's what the help is showing.

A positional does not define the arguments of an optional. The add_argument statements are separate. Omit this add_argument if you aren't defining a positional Action.

In:

parser.add_argument('-a', '--add', help='add sudo item', nargs='*',
                dest="ldap_attrs")

dest specifies the attribute name in args , eg args.ldap_attrs . Without it the attribute would be args.add (the first long flag). And the usage would be

[-a [ADD [ADD ...]]]

I suspect you want to use metavar

parser.add_argument('-a', '--add', help='add sudo item', nargs='*',
                dest="ldap_attrs", metavar=('dn', 'class'))

With a '*', it only accepts 2 metavar strings.