7.7 Polymorphism and type pattern matching

Some functional programming languages offer some clever approaches to the problem of working with statically typed function definitions. The problem is that many functions we’d like to write are entirely generic with respect to data type. For example, most of our statistical functions are identical for int or float numbers, as long as the division returns a value that is a subclass of numbers.Real. The types Decimal, Fraction, and float should all work almost identically. In many functional languages, sophisticated type or type-pattern matching rules are used by the compiler to allow a single generic definition to work for multiple data types.

Instead of the (possibly) complex features of statically typed functional languages, Python changes the approach dramatically. Python uses dynamic selection of the final implementation of an operator based on the data types being used. In Python, we always write generic definitions. The code isn...