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Assuming we want both types of converters in the program we are writing, then this is a bad way of
doing it. It’s bad because we are repeating code. The description method is actually identical, and
__init__ is almost the same. A much better way is to use something called inheritance.
The idea behind inheritance in classes is that when you want a specialized version of a class that
already exists, you inherit all the parent class’s variables and methods and just add new ones or
override the ones that are different. Figure 5-2 shows a class diagram for the two classes, indicating
how ScaleAndOffsetConverter inherits from ScaleConverter, adds a new variable (offset), and
overrides the method convert (because it will work a bit differently).

Figure 5-2 An example of using inheritance
Here is the class definition for ScaleAndOffsetConverter using inheritance:

The first thing to notice is that the class definition for ScaleAndOffsetConverter has
ScaleConverter in parentheses immediately after it. That is how you specify the parent class for a
class.

The __init__ method for the new “subclass” of ScaleConverter first invokes the __init__
method of ScaleConverter before defining the new variable offset. The convert method will
override the convert method in the parent class because we need to add on the offset for this kind of