Higher-Order Functions

A higher-order function is one that takes another function as an argument, returns a function, or both. That single shift, treating functions as values to pass and receive, opens the door to most of Python's functional idioms: sortable collections with custom keys, decorators that wrap behavior, pipelines that compose small transforms, and configurable helpers built by function factories. This lesson covers what counts as higher-order, the patterns common in real Python code, how function composition and pipelines work, how to type them with Callable, and where this style overlaps with object-oriented polymorphism.