Class member function: __init__ , __sub__
class Number: def __init__(self, start): # on Number(start) self.data = start def __sub__(self, other): # on instance - other return Number(self.data - other) # result is a new instance X = Number(5) # Number.__init__(X, 5) Y = X - 2 # Number.__sub__(X, 2) print Y.data # Y is new Number instance