The following class Number implement two methods: constructor and subtraction.
class Number: def __init__(self, start): # On Number(start) self.data = start # from w ww. j ava 2 s. c o m 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