An Extra 'None'

[leoahum]

I'm trying a piece of script from Magnus Lie Hetland's book. It goes as below.

class Person:
    def setName(self, name):
        self.name = name

    def getName(self):
        return self.name

    def greet(self):
        print ("Hello world, I am %s." % self.name)

bar = Person()

bar.setName('Anakin Skywalker')

print (bar.greet())

When I run this script, besides the expected "Hello world, I am Anakin Skywalker", the "print (bar.greet())" gives me an extra line as "None".
Can someone tell me why there is a None?