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Implementation inheritance is the mechanism whereby a subclass re-uses code in a base class. By default the subclass retains all of the operations of the base class, but the subclass may override some or all operations, replacing the base-class implementation with its own.

In the following Python example, subclasses SquareSumComputer and CubeSumComputer override the transform() method of the base class SumComputer. The base class comprises operations to compute the sum of the squares between two integers. The subclass re-uses all of the functionality of the base class with the exception of the operation that transforms a number into its square, replacing it with an operation that transforms a number into its square and cube respectively. The subclasses therefore compute the sum of the squares/cubes between two integers.

Below is an example of Python.

class SumComputer:

def __init__(self, a, b):

self.a = a

self.b = b

def transform(self, x):

raise NotImplementedError

def inputs(self):

return range(self.a, self.b)

def compute(self):

return sum(self.transform(value) for value in self.inputs())

class SquareSumComputer(SumComputer):

def transform(self, x):

return x * x

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