精通Python：利用最佳特性编写高效代码

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"Fluent Python 是一本旨在帮助程序员深入理解并掌握Python编程语言的书籍，由Python Software Foundation成员Luciano Ramalho撰写。本书强调如何编写简洁、高效且具有表现力的Python代码，让读者充分利用Python的最佳特性。作者指出，许多学习Python基础的程序员容易陷入用旧语言思维模式处理Python的陷阱，而这本书则教你如何摆脱这种局限，流畅地编写Python代码。书中涵盖了以下几个关键知识点： 1. **实用的生成器应用**：生成器是Python中的一个重要特性，可以用于数据库处理等场景，使代码更高效，避免一次性加载大量数据。通过生成器，你可以实现迭代过程的惰性计算，有效节省内存。 2. **Python上下文中的设计模式重构**：在Python的语境下重新考虑传统设计模式，例如工厂方法、观察者模式等，以适应Python的特性，如动态类型和鸭子类型。 3. **属性描述符**：理解并掌握属性描述符，这是对象关系映射(ORM)的关键。通过属性描述符，可以控制类的属性访问和行为，实现更加灵活的对象模型。 4. **Pythonic对象**：探讨协议与接口的概念，以及抽象基类和多重继承。Python中，协议允许对象通过实现特定方法来达成某种功能，而无需严格的接口定义。抽象基类和多重继承则提供了扩展和组合类的机制。 5. **深入理解核心语言特性**：书中还涵盖了元类、装饰器、上下文管理器等Python核心概念，这些都是编写高效Python代码的基础。这本书不仅适合有一定Python基础的中级程序员提升技能，也对有经验的Python开发者有所启发。通过阅读《Fluent Python》，你将能够写出更加精炼、性能更好且可读性强的Python代码，从而真正实现Pythonic编程。" 这本书的作者Luciano Ramalho以其丰富的Python编程经验，为读者提供了一条通向Python精通之路，不仅帮助读者提升编程技巧，同时也提供了许多鲜为人知的Python使用技巧。作为Python Software Foundation的成员，他的见解和建议对于任何希望深化Python知识的人来说都是宝贵的财富。

Descriptor Usage Tips 648

Descriptor docstring and Overriding Deletion 650

Chapter Summary 651

Further Reading 679

Afterword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683

A. Support Scripts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687

Python Jargon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715

Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725

xiv | Table of Contents

Python package index now lists more than 60,000 libraries and many of them are in‐

credibly useful.

Who This Book Is For

This book was written for practicing Python programmers who want to become pro‐

ficient in Python 3. If you know Python 2 but are willing to migrate to Python 3.4 or

later, you should be fine. At the time of this writing, the majority of professional Python

programmers are using Python 2, so I took special care to highlight Python 3 features

that may be new to that audience.

However, Fluent Python is about making the most of Python 3.4, and I do not spell out

the fixes needed to make the code work in earlier versions. Most examples should run

in Python 2.7 with little or no changes, but in some cases, backporting would require

significant rewriting.

Having said that, I believe this book may be useful even if you must stick with Python

2.7, because the core concepts are still the same. Python 3 is not a new language, and

most differences can be learned in an afternoon. What’s New in Python 3.0 is a good

starting point. Of course, there have been changes since Python 3.0 was released in 2009,

but none as important as those in 3.0.

If you are not sure whether you know enough Python to follow along, review the topics

of the official Python Tutorial. Topics covered in the tutorial will not be explained here,

except for some features that are new in Python 3.

Who This Book Is Not For

If you are just learning Python, this book is going to be hard to follow. Not only that, if

you read it too early in your Python journey, it may give you the impression that every

Python script should leverage special methods and metaprogramming tricks. Premature

abstraction is as bad as premature optimization.

How This Book Is Organized

The core audience for this book should not have trouble jumping directly to any chapter

in this book. However, each of the six parts forms a book within the book. I conceived

the chapters within each part to be read in sequence.

I tried to emphasize using what is available before discussing how to build your own.

For example, in Part II, Chapter 2 covers sequence types that are ready to use, including

some that don’t get a lot of attention, like collections.deque. Building user-defined

sequences is only addressed in Part IV, where we also see how to leverage the abstract

base classes (ABCs) from collections.abc. Creating your own ABCs is discussed even

xvi | Preface

迁移

later in Part IV, because I believe it’s important to be comfortable using an ABC before

writing your own.

This approach has a few advantages. First, knowing what is ready to use can save you

from reinventing the wheel. We use existing collection classes more often than we im‐

plement our own, and we can give more attention to the advanced usage of available

tools by deferring the discussion on how to create new ones. We are also more likely to

inherit from existing ABCs than to create a new ABC from scratch. And finally, I believe

it is easier to understand the abstractions after you’ve seen them in action.

The downside of this strategy are the forward references scattered throughout the

chapters. I hope these will be easier to tolerate now that you know why I chose this path.

Here are the main topics in each part of the book:

Part I

A single chapter about the Python data model explaining how the special methods

(e.g., __repr__) are the key to the consistent behavior of objects of all types—in a

language that is admired for its consistency. Understanding various facets of the

data model is the subject of most of the rest of the book, but Chapter 1 provides a

high-level overview.

Part II

The chapters in this part cover the use of collection types: sequences, mappings,

and sets, as well as the str versus bytes split—the cause of much celebration among

Python 3 users and much pain for Python 2 users who have not yet migrated their

code bases. The main goals are to recall what is already available and to explain

some behavior that is sometimes surprising, like the reordering of dict keys when

we are not looking, or the caveats of locale-dependent Unicode string sorting. To

achieve these goals, the coverage is sometimes high level and wide (e.g., when many

variations of sequences and mappings are presented) and sometimes deep (e.g.,

when we dive into the hash tables underneath the dict and set types).

Part III

Here we talk about functions as first-class objects in the language: what that means,

how it affects some popular design patterns, and how to implement function dec‐

orators by leveraging closures. Also covered here is the general concept of callables

in Python, function attributes, introspection, parameter annotations, and the new

nonlocal declaration in Python 3.

Part IV

Now the focus is on building classes. In Part II, the class declaration appears in

few examples; Part IV presents many classes. Like any object-oriented (OO) lan‐

guage, Python has its particular set of features that may or may not be present in

the language in which you and I learned class-based programming. The chapters

explain how references work, what mutability really means, the lifecycle of instan‐

Preface | xvii

ces, how to build your own collections and ABCs, how to cope with multiple in‐

heritance, and how to implement operator overloading—when that makes sense.

Part V

Covered in this part are the language constructs and libraries that go beyond se‐

quential control flow with conditionals, loops, and subroutines. We start with gen‐

erators, then visit context managers and coroutines, including the challenging but

powerful new yield from syntax. Part V closes with a high-level introduction to

modern concurrency in Python with collections.futures (using threads and

processes under the covers with the help of futures) and doing event-oriented I/O

with asyncio (leveraging futures on top of coroutines and yield from).

Part VI

This part starts with a review of techniques for building classes with attributes

created dynamically to handle semi-structured data such as JSON datasets. Next,

we cover the familiar properties mechanism, before diving into how object attribute

access works at a lower level in Python using descriptors. The relationship between

functions, methods, and descriptors is explained. Throughout Part VI, the step-by-

step implementation of a field validation library uncovers subtle issues that lead to

the use of the advanced tools of the final chapter: class decorators and metaclasses.

Hands-On Approach

Often we’ll use the interactive Python console to explore the language and libraries. I

feel it is important to emphasize the power of this learning tool, particularly for those

readers who’ve had more experience with static, compiled languages that don’t provide

a read-eval-print#loop (REPL).

One of the standard Python testing packages, doctest, works by simulating console

sessions and verifying that the expressions evaluate to the responses shown. I used

doctest to check most of the code in this book, including the console listings. You don’t

need to use or even know about doctest to follow along: the key feature of doctests is

that they look like transcripts of interactive Python console sessions, so you can easily

try out the demonstrations yourself.

Sometimes I will explain what we want to accomplish by showing a doctest before the

code that makes it pass. Firmly establishing what is to be done before thinking about

how to do it helps focus our coding effort. Writing tests first is the basis of test driven

development (TDD) and I’ve also found it helpful when teaching. If you are unfamiliar

with doctest, take a look at its documentation and this book’s source code repository.

You’ll find that you can verify the correctness of most of the code in the book by typing

python3 -m doctest example_script.py in the command shell of your OS.

xviii | Preface

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