As you have it, the argument ww is expecting a value after -w-w on the command line. If you are just looking to flip a switch by setting a variable True or False, have a look at http://docs.python.org/dev/library/argparse.html#actionhere (specifically store_true and store_false)
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-w', action='store_true')
where action='store_true' implies default=False.
Conversely, you could haveaction='store_false', which implies default=True.