You should quote your vars in the if check, otherwise it doesn't handle spaces very well. (And really the master key should be a master passphrase.)

A few years ago I whipped this up: http://www.thejach.com/public/pw2 (I don't recommend other people use it but it works for me.) I type in something along the lines of "my secret passphrase ycombinator.com". It doesn't do hash iteration and uses the hash as a seed to Python's RNG which I use to get random bytes and then have a password character-space of any printable character -- it also outputs an alpha-numeric version along with different string sizes to handle those dumb sites that put restrictions on your password.