4.1 An overview of function varieties

We need to distinguish between two broad species of functions, as follows:

• Scalar functions: These apply to individual values and compute an individual result. Functions such as abs(), pow(), and the entire math module are examples of scalar functions.

• Collection functions: These work with iterable collections.

We can further subdivide these collection functions into three subspecies:

• Reduction: This uses a function to fold values in the collection together, resulting in a single final value. For example, if we fold + operations into a sequence of integers, this will compute the sum. This can be also be called an aggregate function, as it produces a single aggregate value for an input collection. Functions like sum() and len() are examples of reducing a collection to a single value.

• Mapping: This applies a scalar function to each individual item of a collection; the result is a collection of the same size. The built-in map() function does this...