Python: How to make an option to be required in optparse?

Question

I\'ve read this http://docs.python.org/release/2.6.2/library/optparse.html

But I\'m not so clear how to make an option to be required in optparse?

I\'ve tried to

Answer 1

Since if not x doesn't work for some(negative,zero) parameters,

and to prevent lots of if tests, i preferr something like this:

required="host username password".split()

parser = OptionParser()
parser.add_option("-H", '--host', dest='host')
parser.add_option("-U", '--user', dest='username')
parser.add_option("-P", '--pass', dest='password')
parser.add_option("-s", '--ssl',  dest='ssl',help="optional usage of ssl")

(options, args) = parser.parse_args()

for r in required:
    if options.__dict__[r] is None:
        parser.error("parameter %s required"%r)