Writing higher-order functions in Python

Higher-order functions can be divided into the following three categories.

• Functions that take functions as arguments.
• Functions that return functions, such as the Callable class. Functions that return generator expressions can also be considered higher-order functions.
• Functions that take functions as arguments and return functions, such as functools.partial().

We will use higher-order functions to process simple data, change its structure, and perform the following transformations:

• Packaging data to create more complex objects;
• Extracting components from complex data objects;
• Flattening complex data sequences;
• Structuring one-dimensional data sequences.

Callable class objects are commonly used for functions that return callable objects. We’ll use them later to write functions that can inject configuration parameters.