Python argparse integer condition (>=12) [duplicate]

One way is to use a custom type.

def bandwidth_type(x):
    x = int(x)
    if x < 12:
        raise argparse.ArgumentTypeError("Minimum bandwidth is 12")
    return x

parser.add_argument("-b", "--bandwidth", type=bandwidth_type, help="target bandwidth >= 12")

Note: I think ArgumentTypeError is a more correct exception to raise than ArgumentError. However, ArgumentTypeError is not documented as a public class by argparse, and so it may not be considered correct to use in your own code. One option I like is to use argparse.error like alecxe does in his answer, although I would use a custom action instead of a type function to gain access to the parser object.

A more flexible option is a custom action, which provides access to the current parser and namespace object.

class BandwidthAction(argparse.Action):

    def __call__(self, parser, namespace, values, option_string=None):
        if values < 12:
            parser.error("Minimum bandwidth for {0} is 12".format(option_string))
            #raise argparse.ArgumentError("Minimum bandwidth is 12")

        setattr(namespace, self.dest, values)

parser.add_argument("-b", "--bandwidth", action=BandwidthAction, type=int,
                     help="target bandwidth >= 12")