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Functional Python Programming
Functional Python Programming

Functional Python Programming: Discover the power of functional programming, generator functions, lazy evaluation, the built-in itertools library, and monads , Second Edition

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Functional Python Programming

Introducing Essential Functional Concepts

Most of the features of functional programming are already first-class parts of Python. Our goal in writing functional Python is to shift our focus away from imperative (procedural or object-oriented) techniques to as much of an extent as possible.

We'll look at each of the following functional programming topics:

  • First-class and higher-order functions, which are sometimes known as pure functions.
  • Immutable data.
  • Strict and non-strict evaluation. We can also call this eager versus lazy evaluation.
  • Recursion instead of an explicit loop state.
  • Functional type systems.

This should reiterate some concepts from the first chapter: firstly, that purely functional programming avoids the complexities of an explicit state maintained through variable assignments; secondly, that Python is not a purely functional language.

This book...

First-class functions

Functional programming is often succinct and expressive. One way to achieve it is by providing functions as arguments and return values for other functions. We'll look at numerous examples of manipulating functions.

For this to work, functions must be first-class objects in the runtime environment. In programming languages such as C, a function is not a runtime object. In Python, however, functions are objects that are created (usually) by the def statements and can be manipulated by other Python functions. We can also create a function as a callable object or by assigning lambda to a variable.

Here's how a function definition creates an object with attributes:

>>> def example(a, b, **kw):
...    return a*b
...
>>> type(example)
<class 'function'>
>>> example.__code__.co_varnames
('a&apos...

Immutable data

Since we're not using variables to track the state of a computation, our focus needs to stay on immutable objects. We can make extensive use of tuples and namedtuples to provide more complex data structures that are immutable.

The idea of immutable objects is not foreign to Python. There can be a performance advantage to using immutable tuples instead of more complex mutable objects. In some cases, the benefits come from rethinking the algorithm to avoid the costs of object mutation.

We will avoid class definitions almost entirely. It can seem like anathema to avoid objects in an Object-Oriented Programming (OOP) language. Functional programming simply doesn't need stateful objects. We'll see this throughout this book. There are reasons for defining callable objects; it is a tidy way to provide namespaces for closely related functions...

Strict and non-strict evaluation

Functional programming's efficiency stems, in part, from being able to defer a computation until it's required. The idea of lazy or non-strict evaluation is very helpful. To an extent, Python offers this feature.

In Python, the logical expression operators and, or, and if-then-else are all non-strict. We sometimes call them short-circuit operators because they don't need to evaluate all arguments to determine the resulting value.

The following command snippet shows the and operator's non-strict feature:

>>> 0 and print("right")
0
>>> True and print("right")
right

When we execute the first of the preceding command snippet, the left-hand side of the and operator is equivalent to False; the right-hand side is not evaluated. In the second example, when the left-hand side is equivalent to True...

Recursion instead of an explicit loop state

Functional programs don't rely on loops and the associated overhead of tracking the state of loops. Instead, functional programs try to rely on the much simpler approach of recursive functions. In some languages, the programs are written as recursions, but Tail-CallOptimization (TCO) in the compiler changes them to loops. We'll introduce some recursion here and examine it closely in Chapter 6, Recursions and Reductions.

We'll look at a simple iteration to test a number for being prime. A prime number is a natural number, evenly divisible by only 1 and itself. We can create a naïve and poorly-performing algorithm to determine whether a number has any factors between 2 and the number. This algorithm has the advantage of simplicity; it works acceptably for solving Project Euler problems. Read up on Miller-Rabin...

Functional type systems

Some functional programming languages, such as Haskell and Scala, are statically compiled, and depend on declared types for functions and their arguments. To provide the kind of flexibility Python already has, these languages have sophisticated type-matching rules so that a generic function can be written, which works for a variety of related types.

In Object-Oriented Python, we often use the class inheritance hierarchy instead of sophisticated function type matching. We rely on Python to dispatch an operator to a proper method based on simple name-matching rules.

Since Python already has the desired levels of flexibility, the type matching rules for a compiled functional language aren't relevant. Indeed, we could argue that the sophisticated type matching is a workaround imposed by static compilation. Python doesn't need this...

Familiar territory

One of the ideas that emerged from the previous list of topics is that most functional programming is already present in Python. Indeed, most functional programming is already a very typical and common part of OOP.

As a very specific example, a fluent Application Program Interface (API) is a very clear example of functional programming. If we take time to create a class with return self() in each method function, we can use it as follows:

some_object.foo().bar().yet_more()

We can just as easily write several closely related functions that work as follows:

yet_more(bar(foo(some_object)))

We've switched the syntax from traditional object-oriented suffix notation to a more functional prefix notation. Python uses both notations freely, often using a prefix version of a special method name. For example, the len() function is generally implemented by the __len__...

Learning some advanced concepts

We will set some more advanced concepts aside for consideration in later chapters. These concepts are part of the implementation of a purely functional language. Since Python isn't purely functional, our hybrid approach won't require deep consideration of these topics.

We will identify these up front for the benefit of folks who already know a functional language such as Haskell and are learning Python. The underlying concerns are present in all programming languages but we'll tackle them differently in Python. In many cases, we can and will drop into imperative programming rather than use a strictly functional approach.

The topics are as follows:

  • Referential transparency: When looking at lazy evaluation and the various kinds of optimizations that are possible in a compiled language, the idea of multiple routes to the same object...

First-class functions


Functional programming is often succinct and expressive. One way to achieve it is by providing functions as arguments and return values for other functions. We'll look at numerous examples of manipulating functions.

For this to work, functions must be first-class objects in the runtime environment. In programming languages such as C, a function is not a runtime object. In Python, however, functions are objects that are created (usually) by the def statements and can be manipulated by other Python functions. We can also create a function as a callable object or by assigning lambda to a variable.

Here's how a function definition creates an object with attributes:

>>> def example(a, b, **kw):
...    return a*b
...
>>> type(example)
<class 'function'>
>>> example.__code__.co_varnames
('a', 'b', 'kw')
>>> example.__code__.co_argcount
2

We've created an object, example, that is of the function() class. This object has numerous attributes...

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Key benefits

  • • Learn how to choose between imperative and functional approaches based on
  • expressiveness, clarity, and performance
  • • Get familiar with complex concepts such as monads, concurrency, and immutability
  • • Apply functional Python to common Exploratory Data Analysis (EDA) programming
  • problems

Description

If you’re a Python developer who wants to discover how to take the power of functional programming (FP) and bring it into your own programs, then this book is essential for you, even if you know next to nothing about the paradigm. Starting with a general overview of functional concepts, you’ll explore common functional features such as first-class and higher-order functions, pure functions, and more. You’ll see how these are accomplished in Python 3.6 to give you the core foundations you’ll build upon. After that, you’ll discover common functional optimizations for Python to help your apps reach even higher speeds. You’ll learn FP concepts such as lazy evaluation using Python’s generator functions and expressions. Moving forward, you’ll learn to design and implement decorators to create composite functions. You'll also explore data preparation techniques and data exploration in depth, and see how the Python standard library fits the functional programming model. Finally, to top off your journey into the world of functional Python, you’ll at look at the PyMonad project and some larger examples to put everything into perspective.

Who is this book for?

This book is for Python developers who would like to perform Functional programming with Python. Python Programming knowledge is assumed.

What you will learn

  • • Use Python s generator functions and generator expressions to work with collections in a non-strict (or lazy) manner
  • • Utilize Python library modules including itertools, functools, multiprocessing, and concurrent features to ensure efficient functional programs
  • • Use Python strings with object-oriented suffix notation and prefix notation
  • • Avoid stateful classes with families of tuples
  • • Design and implement decorators to create composite functions
  • • Use functions such as max(), min(), map(), filter(), and sorted()
  • • Write higher-order functions
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Table of Contents

17 Chapters
Understanding Functional Programming Chevron down icon Chevron up icon
Introducing Essential Functional Concepts Chevron down icon Chevron up icon
Functions, Iterators, and Generators Chevron down icon Chevron up icon
Working with Collections Chevron down icon Chevron up icon
Higher-Order Functions Chevron down icon Chevron up icon
Recursions and Reductions Chevron down icon Chevron up icon
Additional Tuple Techniques Chevron down icon Chevron up icon
The Itertools Module Chevron down icon Chevron up icon
More Itertools Techniques Chevron down icon Chevron up icon
The Functools Module Chevron down icon Chevron up icon
Decorator Design Techniques Chevron down icon Chevron up icon
The Multiprocessing and Threading Modules Chevron down icon Chevron up icon
Conditional Expressions and the Operator Module Chevron down icon Chevron up icon
The PyMonad Library Chevron down icon Chevron up icon
A Functional Approach to Web Services Chevron down icon Chevron up icon
Optimizations and Improvements Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Half star icon Empty star icon 3.7
(3 Ratings)
5 star 66.7%
4 star 0%
3 star 0%
2 star 0%
1 star 33.3%
Jerome3590 Sep 05, 2018
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Author does a great job of walking through both the how and why of python's functional programming capabilities. First programming book I've read that actually details the implementation of the code and what it's doing. I do not have a computer science background and the author's format and explanations for how the code works behind the scenes I found extremely insightful. This will be a book I routinely refer to. I will definitely check out Steven Lott's other books!
Amazon Verified review Amazon
Jonathan Davis Jan 09, 2021
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Having had experience with functional programming before, I was pleased that this book covered all the concepts and did so clearly.
Amazon Verified review Amazon
AmazonReviewer Mar 24, 2020
Full star icon Empty star icon Empty star icon Empty star icon Empty star icon 1
If this is functional programming, then it sucks. It makes everything difficult and more complex than it needs to be, which makes it hard to create-read-understand-maintain. I fail to see the point. It is not practical.
Amazon Verified review Amazon
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