class User(object):
    MALE = 0
    FEMALE = 1
    GENDERS = [(MALE, 'Male'), (FEMALE, 'Female')]

    def __init__(self, gender):
        self.gender = gender

    def greet(self):
        return {MALE: 'Hi, boy', FEMALE: 'Hi, girl.'}[self.gender]

alex = User(0)
print alex.greet()