Beginning Python：Using Python 2.6 and Python 3.1

Part I

Dipping Your Toe into Python

Chapter 1:Programming Basics and Strings

Chapter 2: Numbers and Operators

Chapter 3:Variables — Names for Values

Programming Basics and Strings

This chapter is a gentle introduction to the pradtice of programming in Pythan.Python is avery rich language with manyfeatures,so it is important tolearn towalk before you learn torun. Chapters 1 through 3 provide a basic introduction to oommon programming ideas, explained in easily digestible paragraphs with simple examples.

If you are already an experienced programmer interested in Python, you may want to read this chapter quickly and take note of the examples,but untilChapter 3 you will be reading material with which you've probably already gained some familiarity in another language.

If you are a novice programmer, by the end of this chapter you will learn the following:

口 Some guiding prindples for programming

口 Directions for your first interactians with a programming language —Python. The exerdises at the end of thechapter provide hands-on experience with the basic information that you have learned.

How Programming is Different from Using a Computer

The first thing you need to understand about computers when you're programming is that you control the computer. Sometimes the computer doesn't do what youexpect, but even when it doesn't do what vou want the first time.itshould dothe same thing the segnd and third time —until you take dharge and change the program.

The trend in personal computers has been away from reliability and toward software being built on top of other,unreliable, software. The results that you live with might have you beliewing that computers are malicious and arbitrary beasts,existing totaunt wou with umnbearable amounts of extra wark and various harassments while you're already trying toaccomplish something,However, after you've learned how to program, you gain an understanding of how this situation has come to pas,and perhaps yau'll find that you can do better than some of the programmers whose software you've used.

Note that programming in a language like Python, an inferprefed language, means that you are not going to need to know a whole lot about computer hardware, memory,or long sequences of 0sand ls.You are going to write in text form like you are used to reading and writing but in a different and simpler languge.Pythan is the language, and like English orany other Language(s) you speak.it makes sense to other people who already speak the language. Learninga programming language can be even easier, howeverbeause programming languages aren't intended for discussions,debates, phone calls, plays, movies, or any kind of casulinteraction.They're intended for givinginstrudtions and ensuring that those instructions are followed.Computers have been fashianed into incredibly flexible tools that have found a use in almost every business and task that people have found themselves doing,but they are still built from fundamentally understandable and controllable pieæs.

Programming is Consistency

In spite of the complexity involved in coveringall of the disciplines into which computers have crept, the basic cmputer is still relatively simple in prinaple. Theinternalmschanisms that definehow a compuer works haven't dhanged a lot since the 1950s when transistors were first used in computers.

In all that time,this core simplicity has meant that computers can,and should, be held to a high standard of consistency. What this means to you, as the programmer, is that anytime you tell a computer to metaphorically jump,you must tell ithow high and where to land. and it will perform thatjump—over and over again for as long as you specify. The program should not arbitrarily stop working orchange how it works without you facilitating the change.

Programming is Control

Programminga computer is very different from creatinga program,as the word applies to people in real life. In reallife,you ask people to do things,and sometimes you have to struggle mightily toensre that your wishes are carried out— for example, if you plan aparty for 30people and assign two of them to bring the chips and dip and they bring thedrinks instead, it is out of your control.

With computers that problem doesn't exist. Thecomputer does exactly what you tell it to do.As you can imagine, this means that you must pay some attention to detail to ensure that thecomputer does just what you want it to do.

One of the goals of Python is to program inblocks that enable you to think about larger and larger prgjects by building each project as pieces that behave in well-understood ways, This is a key goal of a programmingstyle known as objec-orientfed programming.The guiding principle of this style is that you can create reliable pieæs that still workwhen you pieg them together，that are understandable.and that are useful.This gives you,the programmer, control over how the parts of your programs run, while enabling you toextend your program as the problems you're solving evolve.

Programming Copes with Change

Programs are run on computers that handle real-world problems; and in the real world, plans and circumstancs frequently change. Because of these shifting circumstanæs， programmers rarely get the opportunity to create perfectly crafted, useful, and flexible programs.Usually, you an achieveonly two of these gols.The dhanges that you will have to deal with should give you some perspective andlead you to program cautiously. With sufficient caution, you can create programs that know when they're being asked to ewceed their capabilities,and they can fail graafully by notifying their users that they've stopped.In the best cases, you can create programs that explain what failed and why. Python offers especially useful features thatenable you to describe what conditians may have occurred that prevented your program from working.

What All That Means Together

Taken together, these beginning principles mean that you're going to be introduced toprogramming as a way of tellinga computer what tasks you want it todo,in an environment where you are in control. You will be aware that sometimes accidents can happen and that these mistakes can be accommodated through mechanisms that offer you some discretion regarding how these conditions will he handled including recowering from problems and continuing to work.

The First Steps

The absolute first step you need to take before you can begin programming in Python is to download and install Python version 3.1.Navigate towww.python .org/downioad and choose the newest yersion of Python.You will be taken toa page with instructions on how to download the appropriate version far your computer.For instance,if you are running Windows, it may say Windows x86MSTInstaller(.0).

Just as authors and editors have specialized tools for writing for magazines, books,or online

publications.programmers also need specialized tools.Asa starting Python programmer. the right tool for the job is the Pythan IDLE GUI (graphicaluser interface).

One the download is finished，double-click it to run the program.Your best bet is to acæpt the default prompts Python offers you. This procss may take a few minutes,depending on your system.

After setup is complete,you will want to test to make sure it is installed properly Click the Windows Start menu and go to All Programs.You will see Pythan 3.0in themenu.ChooseIDLE ((Python GUI) and wait for the program to load.

【下载地址】

链接：https://pan.baidu.com/s/1X-Bbn5ckXw9Yhv6JXYXQgA

提取码：8031