Python 3编程入门指南

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"Apress - Python 3 for Absolute Beginners (October 2009) (ATTiCA).pdf" 是一本面向初学者的Python编程入门教材，由Tim Hall和J-P Stacey共同撰写。这本书旨在帮助没有编程背景的读者快速理解和掌握Python 3的主要功能，适合初级水平的学习者。本书内容覆盖了Python 3的基础知识，包括但不限于： 1. **Python语言基础**：讲解Python的基本语法，如变量、数据类型（整型、浮点型、字符串、列表、元组、字典等）、运算符、流程控制（条件语句、循环结构）等。 2. **函数和模块**：介绍如何定义和使用函数，以及如何组织代码为模块，以便于代码复用和项目管理。 3. **面向对象编程**：解释面向对象的概念，包括类的定义、对象的创建与操作、继承、多态等核心概念。 4. **异常处理**：教授如何在程序中捕获和处理错误，以增强程序的健壮性。 5. **文件操作**：教授如何读写文件，进行基本的输入输出操作，这是许多实际应用中的常见需求。 6. **标准库和第三方库**：介绍Python标准库中的常用模块，如os、sys、datetime等，并引导读者了解如何使用第三方库，如numpy、pandas等，以扩展Python的功能。 7. **调试和测试**：教授基本的调试技巧和编写测试用例的方法，帮助读者确保代码的正确性。 8. **实践项目**：书中可能包含一些小型的编程项目，让读者将所学知识应用于实际问题中，提升编程技能。此外，这本书还强调了解决实际问题的能力，鼓励读者运用逻辑思维解决问题，而不仅仅是学习语法。书中可能提供配套的电子书版本和源代码，方便读者在线阅读和实践。通过阅读和实践《Python 3 for Absolute Beginners》，读者将能够建立起坚实的编程基础，为进一步学习更复杂的编程概念和技术打下坚实的基础。无论你是打算从事数据分析、Web开发还是自动化任务，这本书都将是你开启Python编程之旅的理想起点。

C H A P T E R 1

■ ■ ■

Introducing Python

So, you want to learn programming. Welcome to one of the great adventures of the twenty-first century.

Programming requires little in the way of specialized equipment; the software tools can all be

downloaded for free off the Internet, and it can be practiced in the safety and comfort of your own home,

without having to ask anyone’s permission. This chapter will ease you in gently by introducing you to the

software you will need to create your programs: a command-line interface, which allows you to use

Python in interactive mode, and a text editor for writing scripts—nothing more complicated than that. I

will also show you where to go to find help and documentation, so you can decode the sometimes-

impenetrable jargon that seems to surround this, the geekiest of all technical disciplines. To begin with,

you will need to make sure that you have a decently recent version of Python installed on your machine

or follow the steps later in this chapter to install it (see “Choosing the Right Python Version” for a

definition of decently recent). This chapter explains how to make sure that you have everything set up

correctly and that you have suitable references at hand before you start your journey.

Python is an excellent language with which to learn programming. There are many reasons for this,

but the simple explanation is that it’s easy to read and fast to write; it doesn’t take long to come up with

working code that does something meaningful. Python has a very human-friendly syntax, which makes

writing elegant code easy. The basic language is fairly simple and therefore easy to remember, and then

it has an extensive library of predefined functions that you can use to facilitate most common computer

tasks. Writing effective applications in Python can be as simple as playing with conceptual building

blocks. It works really well for writing a little two-line application to perform some routine system

administration task or to provide interactive functions on a web page, but it has enough power and

flexibility to comfortably create much larger and more complex applications with graphic interfaces

indistinguishable from the programs you are used to running from your computer’s main menu. If you

follow the suggestions laid out in this book about writing self-explanatory code, in several months, even

years, you will be able to come back to your programs and see immediately what they were supposed to

do and what your original intentions were; this makes maintaining programs much simpler too.

OK, let’s make sure your system is ready for you to start running Python programs.

Running Python on Various Systems

Python can be installed and run on most operating systems including Windows, Mac OS X, or OS/2,

Linux, and Unix. If you are running Mac OS X or a GNU/Linux system, you will probably have it installed

by default. I would recommend using a system of this kind, which already has Python set up as an

integral part. The book was written using a Debian GNU/Linux system, and therefore, the examples will

CHAPTER 1 ■ INTRODUCING PYTHON

work exactly the same on any Debian-based system, such as Ubuntu. In fact, the differences between

Linux variants are few, so you’ll be equally at home with other distributions.

Installing on Windows

If you are using Windows, you will probably have to install Python and configure certain settings

correctly before you can get to grips with the examples in this book. For that, you will need to refer to the

specific instructions for your operating system on the following Python web pages:

• http://wiki.python.org/moin/BeginnersGuide/Download

• http://www.python.org/doc/faq/windows/

• http://docs.python.org/dev/3.0/using/windows.html

First, you need to download the official installer; alternative versions for Itanium and AMD

machines are available from http://www.python.org/download/. You should save this file, which will

have a .msi extension, somewhere you’ll be able to find again easily. You can then double-click this file

to start the Python installation wizard, which will take you through the installation. It’s fine to accept the

default settings if you’re not sure of any answer.

Installing on Other Systems

You may choose to install Python on other systems, particularly if you want to take advantage of newer

versions. For Linux and other Unix-like systems, the installation instructions are here:

• http://docs.python.org/dev/3.0/using/unix.html

If you’re using OS X, your instructions are here:

• http://www.python.org/download/mac/

• http://docs.python.org/dev/3.0/using/mac.html

Choosing the Right Python Version

You will find the different installers include a number after the word Python. This is the version number.

When I started writing this book, those numbers ranged from 2.3.7 (old but still usable) through 2.5.2

(the previous stable version) to 3.0 (the new version about to be released). At the same time as version

3.0 was released, the Python team also put out version 2.6, which is an upgraded version of Python

version 2 for people who want (or need) to stick with the old way of doing things but still want to benefit

from general fixes and some of the new features introduced in version 3.0.

The Python language is continuously evolving; version 3.0 has become the norm and has evolved

into version 3.1.1. The new version, which I’ll refer to as version 3.0 because all 3.x versions are simply

refinements on the original plan of 3.0, includes several changes to the programming language that are

incompatible with version 2.x (x is any number you like), which I will refer to in the rest of this book as

the old version. Most of the language is the same, however, so the differences between the versions of

Python will be noted in the text as those subjects are covered. Examples in this book are for Python 3.0

except where noted.

CHAPTER 1 ■ INTRODUCING PYTHON

Further information about the latest version of Python 3.0 (also known as Py3k or Python 3000) is

available at http://www.python.org/download/releases/.

There may be some differences running Python on other operating systems, which I will do my best

to point out where relevant. Otherwise, the examples of code will work the same way. This is one of the

many good points of Python. For the most part, this book will concentrate on the fun part—learning how

to write programs using Python. The official Python documentation is plentiful, free, and well written,

and you should read it alongside this book. It is available on at http://www.python.org/doc/.

Understanding the Jargon

Throughout this book, I will be doing my best to demystify, clarify and explain the various bits of technical

terminology that you will frequently encounter during the process of learning the art of programming.

Technical terms and jargon words that need further explanation will be highlighted in bold the first time

you encounter them. Any terms not immediately explained in the chapter will be covered in the “Jargon

Busting” section at the end of each chapter. You may also wish to study one of the most famous resources

on the Internet, the Jargon File, which is part of the New Hacker’s Dictionary (available at

http://catb.org/~esr/jargon/).

As an example, here’s the definition of the noun “code” from the Jargon File:

“The stuff that software writers write, either in source form or after translation by a compiler or assembler.

Often used in opposition to ‘data,’ which is the stuff that code operates on. Among hackers this is a mass

noun, as in ‘How much code does it take to do a “bubble sort”?’ or ‘The code is loaded at the high end of

RAM.’ Among scientific programmers, it is sometimes a count noun equivalent to ‘program;’ thus they may

speak of ‘codes’ in the plural. Anyone referring to software as ‘the software codes’ is probably a ‘newbie’

or a ‘suit’.”

For comparison’s sake, here’s the definition of the verb “code”:

“To write code. In this sense, always refers to source code rather than compiled. ‘I coded an Emacs clone

in two hours!’ This verb is a bit of a cultural marker associated with the Unix and minicomputer traditions

(and lately Linux); people within that culture prefer v. ‘code’ to v. ‘program,’ whereas outside it, the reverse

is normally true.”

The noun “program” is defined as being:

• “A magic spell cast over a computer allowing it to turn one’s input into error

messages”

• “An exercise in experimental epistemology”

• “A form of art, ostensibly intended for the instruction of computers, which is

nevertheless almost inevitably a failure if other programmers can’t understand it”

As the information contained in the Jargon File is more entertaining than strictly informative, I will be

providing some simpler definitions at the end of each chapter.

CHAPTER 1 ■ INTRODUCING PYTHON

Learning While Having Fun

Having fun is often underestimated in the realm of technical disciplines. We learn best and are most

productive when we’re having fun. Developing software using Python is often an engrossing and

enjoyable experience, partly because you can test out your changes as soon as you have made them

without having to perform any intermediary steps.

Python also deals with many background tasks, the household chores of programming, so you don’t

have to bother with them as you might in languages like C. This kind of immediate gratification makes it

easier to stay in the creative flow and keep being inspired.

Python is also easy to read, being closer to natural language than many other programming

languages, so you spend less time trying to decode what you have just written, which in turn means

more time to think about how you could improve and expand your work.

The other great thing is that you can use Python for pretty much any task you can think of, be it large

or small, simple text-driven script or major graphical application. It does have its limitations, but by the

time you come up against them, you will already have become a competent programmer and will be

able to make an informed choice about where to go next.

Introducing the Interactive Shell

Although this book is primarily aimed at showing you how to write stand-alone scripts and

applications—that is, fully fledged programs that don’t require anything other than having Python

installed for them to work—Python also works in interactive mode, which allows you to enter Python

commands using a command-line interface. This is a great resource for immediate Python gratification.

You need to locate and start up your computer’s command-line interface, sometimes known as the

terminal or terminal emulator, or on machines running Windows, the DOS prompt. This will provide

you with a command line at which you can start typing commands. Interactive mode can be started up

by typing python at the command line. If Python is properly installed, you should see something like this:

$ python

Python 3.1.1 (r311:74483, Aug 17 2009, 17:02:12)

[GCC 4.2.3 (Debian 4.2.3-5)] on linux2

Type "help", "copyright", "credits" or "license" for more information.

>>>

The details may be different according to your operating system. The first line shows the Python

version number and the compilation date of the version you have installed. The last line (>>>) is your

Python prompt. This indicates that the Python interpreter is running and waiting for your input. The

Python interpreter is the program that reads Python programs and carries out their instructions.

Interactive mode can be useful for testing out individual commands line by line, experimenting with

new ideas, and getting help (try typing help(), and don’t forget the parentheses; they are important). To

get out of the interactive Python interpreter on a Linux system, you can use the quit() or exit()

functions, or else you must hold down the Ctrl key and the D key at the same time (in Windows, you

need to use Ctrl+Z and then press Enter).

CHAPTER 1 ■ INTRODUCING PYTHON

Choosing to Code with a Text Editor

My preferred method of creating Python scripts is to use a plain text editor, with a few basic

programming features. Programs like notepad (especially notepad2/++), BBedit, gedit, NEdit and Kate

are ideal for this task. A variety of editors are available that offer specific enhancements for

programmers, such as syntax highlighting, which is useful for showing coding errors immediately as you

type. Old-school hackers may prefer to use Vi or Emacs. Python does not dictate what software you use

to create the code; the choice is up to you. Do not attempt to use word-processing software, such as

Word or OpenOffice for this task; it will mess you up badly. Be warned!

Choosing to Code with an Integrated Development

Environment

An integrated development environment (IDE) is a graphical interface with lots of useful features

designed to make programming with Python even easier. You still have to type the code in the same way,

but you can do all your coding using a single application, and these programming environments can

provide some useful shortcuts and reminders. There are now several Python-specific IDEs. Popular

applications include IDLE (which is bundled with Python itself), Eric (you may notice a theme here,

nudge nudge, wink wink, say no more...), Geany, DrPython, and SPE. Python is also supported by more

general programming environments like Bluefish and a whole host of others. This book doesn’t cover

the use of IDEs or any of the alternative distributions of Python, because each of these approaches

would require a chapter unto themselves, at the very least. However, the examples contained in this

book will still work if you do choose to explore these options. This book will take the simplest approach,

using tools that come as standard with most operating systems; that is, a text editor and the Python

Interactive Shell.

Getting Started with Programming

The process of writing a new program usually starts with a problem. Before you can code anything, you

need to have an idea of what you want to create, the problem you wish to solve, and a fairly good idea of

how to solve it. Chapter 2 will take you through the process of designing software, known as the software

development cycle. Usually, this is something that you have to learn separately, as most programming

manuals go straight into the details of the language, assuming you will have studied program design at

college or in the process of learning some other programming language. This can lead you to create code

that is difficult to read and understand and makes fixing problems later a nightmare. Understanding the

principles of software design can dramatically speed up the process of creating new software and help

ensure that important details are not missed out.

In Chapter 3, you start coding those designs in Python. You will learn about constructing the basic

units of data, words and numbers, and how to combine and manipulate them. In Chapter 4, I will show

you how to compare values, make choices, and deal with errors. The subsequent chapters go through

the process of refining those designs, breaking them down into manageable chunks, and expanding your

understanding of the Python programming language so you can turn your ideas into fully fledged,

functional computer programs.

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