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Functional programming offers a variety of techniques for creating succinct and expressive software. While Python is not a purely functional programming language, we can do a great deal of functional programming in Python. Python has a core set of functional programming features. This lets us borrow many design patterns and techniques from other functional languages. These borrowed concepts can lead us to create elegant programs. Python’s generator expressions, in particular, negate the need to create large in-memory data structures, leading to programs that may execute more quickly because they use fewer resources. We can’t easily create purely functional programs in Python. Python lacks a number of features that would be required for this. We don’t have unlimited recursion, for example, we don’t have lazy evaluation of all expressions, and we don’t have an optimizing compiler. There are several key features of functional programming languages that are available in Python. One of the most important ones is the idea of functions being first-class objects. Python also offers a number of higher-order functions. The built-in map(), filter(), and functools.reduce() functions are widely used in this role, and less obvious are functions such as sorted(), min(), and max(). In some cases, a functional approach to a problem will also lead to extremely highperformance algorithms. Python makes it too easy to create large intermediate data structures, tying up memory (and processor time). With functional programming design patterns, we can often replace large lists with generator expressions that are equally expressive but take up much less memory and run much more quickly. We’ll look at the core features of functional programming from a Python point of view. Our objective is to borrow good ideas from functional programming languages and use those ideas to create expressive and succinct applications in Python. This book is for more experienced programmers who want to create succinct, expressive Python programs by borrowing techniques and design patterns from functional programming languages. Some algorithms can be expressed elegantly in a functional style; we can—and should—adapt this to make Python programs more readable and maintainable. This is not intended as a tutorial on Python. This book assumes some familiarity with the language and the standard library. For a foundational introduction to Python, consider Learn Python Programming, Third Edition: https://www.packtpub.com/product/learn-p ython-programming-third-edition/9781801815093. While we cover the foundations of functional programming, this is not a complete review of the various kinds of functional programming techniques. Having an exposure to functional programming in another language can be helpful.