In this segment, you learn how to define binary methods and you learn how to define your own numberlike classes.

In particular, you learn how to define a Weight class, so that you represent weight quantities explicitly, using Weight instances, rather than implicitly, using instances of one of the number classes. The Weight class has some numberlike properties, such as answering to magnitude-comparison, addition, and subtraction methods, buts lack others, such as answering to exponentiation methods. Thus, the Weight class is reminiscent of the built-in Time and Date classes, which you learned about in Chapter 26.