作为一个正在努力的程序员看了这篇文章之后思考了非常多，虽然是很久之前的文章了，所使用的技术也已经不断地革新，但是文章背后所传递的思想真的非常深刻而有建设性。学习编程真的不是21天24hours的事情，我也特别讨厌周围或者网络上的人报了一个班学了一些知识就在那里装大牛，其实内里一点都经不起推敲。希望有志之士可以看看这篇传世之文，你一定会有所收获的。
原文：http://norvig.com/21-days.html
译文：http://daiyuwen.freeshell.org/gb/misc/21-days-cn.html
目录
英文版 Teach Yourself Programming in Ten Years
Why is everyone in such a rush?
Teach Yourself Programming in Ten Years
So You Want to be a Programmer
Appendix: Books and Other Resources
中文版 十年学会编程
为何人人都这么着急？
信步走进任何一家书店，你会看到名为《如何在7天内学会Java》的书，还有各 种各样类似的书： 在几天内或几小时内学会Visual Basic, Windows, Internet等等，一眼望不到 尽头。我在Amazon 上做了如下的 强力检索 ：
pubdate: after 1992 and title: days and (title: learn or title: teach yourself)
得到了248个结果。前78个都是计算机类书籍（第79个是 Learn Bengali in 30 days）。我用"hours"替换"days"，得到了类似的结果： 更多的253书。前77本是计算机类书籍，第78本是 Teach Yourself Grammar and Style in 24 Hours。在前200本书中，有96% 是 计算机类书籍。
结论是：要么人们都在急急忙忙地学习计算机，要么计算机比其它任何东西都 容易学。没有书籍教你在几天内学会古典音乐、量子物理，或者是养狗。
让我们分析一下，象一本名为《三天内学会Pascal》的书意味着什么：
- 学习： 在三天里，你没有时间写一些重大的程序，并从成功或失败中 得益。你没有时间与有经验的程序员合作，并理解在那样的环境下工作是怎么回 事。一句话，你不会有时间学到太多东西。因此他们只能谈论一些肤浅的东西，而 不是深入的理解。正如亚力山大教皇所说，浅尝辄止是危险的事情。
- Pascal： 在三天时间里，你可能学会Pascal的语法（如果你 已经学过类似的语言），但你学不到更多的如何使用这些语法的知识。也就是说， 假如你曾是个BASIC程序员，你可以学着用Pascal语法写出BASIC风格的程序，但你不 可能了解Pascal真正的好处（和坏处）。那么关键是什么？Alan Perlis 说过：“一种不改变你编程的思维方式的语言，不值得去学。” 一种可 能的情况是：你必须学一点儿Pascal（或可能性更大的象Visual Basic 或 JavaScript之类），因为你为了完成某种特定的任务，需要与一个现存的工具建立 接口。不过那不是学习如何编程，而是在学习如何完成那个任务。
- 三天内： 很不幸，这不够，原因由下一节告诉我们。
在十年里学会编程
研究表明 (Hayes，Bloom)在 任何一种领域内，象下棋、作曲、绘画、钢琴演奏、游泳、网球、以及原子物理学和拓 扑学，等等，要达到专家水平大约都要化十年时间。没有真正的捷径：即使是莫扎 特，4岁时就是音乐神童，13年后才开始写出世界级的作品。在另一方面，披头 士似乎在1964年的Ed Sullivan表演上一炮走红。但他们从1957年就开始表演，在 获得大众青睐后，他们的第一个重大成功，Sgt. Peppers，是1967年发 行的。Samuel Johnson （塞缪尔·约翰逊，英国辞典编纂家及作家）认为要花比十年更长的时间：“在任何领域中出类拔萃都 要用毕生的劳作来取得；它不可能用较低的代价获得。” 而Chaucer（乔叟，英 国诗人）感叹到：“人生短暂，学海无涯。”
这是我为编程成功开出的方子：
- 设法对编程感兴趣，并且因为它有趣而编一些程序。确保编程一直充满足够 乐趣，这样你才愿意投入十年宝贵时间。
- 与其他程序员交流； 阅读其它程序。这比任何书本或训练课程都 重要。
- 写程序。 最好的学习方式是 从实 践中学习。 用更技术性的话说，“在一个给定的领域内，个人的最大能力不 是自动地由扩展了的经验取得的，但即使是高度有经验的人也可以通过有意识的 努力来提高自己的能力” (p. 366) 和 “最有效的学习需要因人而异的适当难度，目标明确的任务，丰富的信息反 馈，以及重复的机会和错误修正。” (p. 20-21) 此书 Cognition in Practice: Mind，Mathematics，and Culture in Everyday Life是阐明此观点的令人感兴趣的参考文献。
- 如果愿意，在大学里呆上4年或更长（在研究生院里）。你会接触到 一些需要学历证明的工作，你会对此领域有更深的理解。如果你不喜欢学校， 你可以（通过一 些贡献）在工作中获得相似的经验。在任何情况下，光啃书本是不够的。Eric Raymond，The New Hacker's Dictionary一书的作者，说过，“计算机科学不能把任何人变成编程 专家，就象光研究刷子和颜料不会使人变成画家一样。” 我雇佣过的最好的程序员 之一仅有高中程度；他做出了许多优秀的 软件，有他自己的新闻组， 而且通过股票期权，他无疑比我富有的多。
- 和其他程序员一起做项目。在其中的一些项目中作为最好的程序 员； 而在另一些项目中是最差的。当你是最好的，你能测试领导项目的能力，用你 的观点激发别人。当你是最差的，你学习杰出者是怎么做的，了解他们不喜欢做 什么（因为他们吩咐你做事）。
- 在其他程序员 之后接手项目。使自己理解别人写的程序。 当程序的原作者不在的时候，研究什么需要理解并且修改它。思考如何设计你的 程序以便后来者的维护。
- 学习至少半打的编程语言。包括一种支持类抽象的语言（象Java 或C++），一种支持函数化抽象的语言（象Lisp或ML），一种支持语法抽象的语 言（象 Lisp），一种支持声明规格说明的语言（象Prolog或C++ 的模板），一种支持 共行程序（coroutine）的语言（象Icon或Scheme），一种支持并行的语言（象Sisal）。
- 请记住“计算机科学”中有“计算机”一词。了解你的计算机要花多 长时间执行一条指令，从内存中取一个字（有cache），从磁盘中读取连续的字， 和在磁盘中找到新的位置。（答案）
- 参与一种语言标准化的工作。它可以是ANSI C++委员会， 也可以是决定你周围小范围内的编程风格是应该两个还是四个空格缩进。通 过任何一种方式，你了解到其他人在某种语言中的想法，他们的理解深度，甚至一 些他们这样想的原因。
- 找到适当的理由尽快地从语言标准化的努力中脱身。
明白了这些，仅从书本中你能得到多少就成了一个问题。在我第一个孩子出生前， 我读了所有的（关于育儿的）How to 书籍，仍然感觉是个手足无措的新手。30个月以后，我 的第二个孩子快要出生了，我回头温习这些书了吗？ 没有。相反，我依靠我的个人 经验，它比专家写的数千页书更有用和可靠。
Fred Brooks在他的随笔 《没有银弹》 中定出了一个寻找优秀软件设计者的三步计划：
- 尽可能早地，有系统地识别顶级的设计人员。
- 为设计人员指派一位职业导师，负责他们技术方面的成长，仔细地为他们规划 职业生涯。
- 为成长中的设计人员提供相互交流和学习的机会。
此计划假设某些人已经具备了杰出设计者的必要才能； 要做的只是如何恰当地诱 导他们。 Alan Perlis 说得更简明扼要：“每个人都能被教会雕刻：对米开朗其罗而言， 反倒是告诉他哪些事不要做。同样的道理也适用于优秀的程序员。”
所以尽管买那本Java的书吧。你可能会从中学到点儿东西。但作为一个程序员，你不会在 几天内或24小时内，哪怕是几个月内改变你的人生，或你实际的水平。
参考文献
Bloom, Benjamin (ed.) Developing Talent in Young People, Ballantine, 1985.
Brooks, Fred, No Silver Bullets, IEEE Computer, vol. 20, no. 4, 1987, p. 10-19.
Hayes, John R., Complete Problem Solver Lawrence Erlbaum, 1989.
Lave, Jean, Cognition in Practice: Mind, Mathematics, and Culture in Everyday Life, Cambridge University Press, 1988.
答案
2001年夏天典型的1GHz PC的各种操作要花的时间
| 执行一条指令 | 1 nsec = (1/1,000,000,000) sec |
| 从L1 cache memory 中取一个字 | 2 nsec |
| 从内存中取一个字 | 10 nsec |
| 从磁盘的连续位置取一个字 | 200 nsec |
| 从磁盘的新位置取一个字(seek) | 8,000,000nsec = 8msec |
附录：语言的选择
不少人问我，他们首先该学哪种编程语言。没有绝对的答案，不过请考虑以下几 点：
- 用你的朋友的。当被问起“我该用哪种操作系统，Windows，Unix， 还是Mac？”，我总是回答：“你朋友用什么，你就用什么。” 你从朋友那能学 到知识，这种优势可以抵销不同操作系统或语言之间本质的差异。也考虑你将来 的朋友：程序员社区 — 你将成为它的一部分如果你继续往前走的话。你选择的 语言是否有一个成长中的社区，还是人数不多、即将消亡？ 有没有书籍、网站、 在线论坛回答你的问题？ 你喜欢论坛里的那些人吗？
- Keep it simple, stupid. 象C++和Java这样的语言是为经验丰富的 程序员组成的团队进行专业开发而设计的，他们专注于代码运行时的效率。因此， 这些语言有些部分非常复杂。 而你关注的是如何编程，不需要那些复杂性。你 需要的是这样的语言： 对单个的编程新手来说，它易学易记。
- 练习。你偏爱哪种学弹钢琴的方式：通常的交互式的方式，你一 按下琴键就能听到音符；还是“批量”模式，你只有弹完整首曲子才能听到音符？ 显然，用交互模式学习弹钢琴更容易些，编程也一样。坚持用交互模式学习并使 用一种语言。
有了上面的准则，我推荐的第一个编程语言是Python或Scheme。因人而异，还有其它 好的选择。如果你的年纪是10岁以下，你可能更喜欢Alice。关键是你要选择并开始实践。
附录：书籍和其它资源
不少人问我，他们该从什么书籍或网页开始学起。我重申“仅从书本里学习是不 够的。” 但我还是推荐：
- Scheme: Structure and Interpretation of Computer Programs (Abelson & Sussman)可能是最好 的计算机科学的入门书，而且它的确把讲授编程作为理解计算机科学的一种方法。 但它具有挑战性，会让许多通过其它方式可能成功的人望而却步。
- Scheme: How to Design Programs (Felleisen et al.)是关于如何用一种优美的、函数化的方式设 计程序的最好的书之一。
- Python: Python Programming: An Intro to CS (Zelle)是优秀的Python入门指导。
- Python: Python.org上有许多在线指导。
- Oz: Concepts, Techniques, and Models of Computer Programming (Van Roy & Haridi) 被视为Abelson & Sussman的当代继承者。它是对编程的高层次概念的巡视。 涉及的范围比Abelson & Sussman更广，同时可能更容易学习和跟进。 它用了叫 做Oz的语言，不太知名，却可以作为学习其它语言的基础。
脚注
This page also available in Japanese translation thanks to Yasushi Murakawa, in Spanish translation thanks to Carlos Rueda and in German translation thanks to Stefan Ram.
T. Capey points out that the Complete Problem Solver page on Amazon now has the "Teach Yourself Bengali in 21 days" and "Teach Yourself Grammar and Style" books under the "Customers who shopped for this item also shopped for these items" section. I guess that a large portion of the people who look at that book are coming from this page.
英文版 Teach Yourself Programming in Ten Years
Peter Norvig
Why is everyone in such a rush?
Walk into any bookstore, and you'll see how to Teach Yourself Java in 24 Hours alongside endless variations offering to teach C, SQL, Ruby, Algorithms, and so on in a few days or hours. The Amazon advanced search for [title: teach, yourself, hours, since: 2000 and found 512 such books. Of the top ten, nine are programming books (the other is about bookkeeping). Similar results come from replacing "teach yourself" with "learn" or "hours" with "days."
The conclusion is that either people are in a big rush to learn about programming, or that programming is somehow fabulously easier to learn than anything else. Felleisen et al. give a nod to this trend in their book How to Design Programs, when they say "Bad programming is easy. Idiots can learn it in 21 days, even if they are dummies." The Abtruse Goose comic also had their take.
Let's analyze what a title like Teach Yourself C++ in 24 Hours could mean:
- Teach Yourself: In 24 hours you won't have time to write several significant programs, and learn from your successes and failures with them. You won't have time to work with an experienced programmer and understand what it is like to live in a C++ environment. In short, you won't have time to learn much. So the book can only be talking about a superficial familiarity, not a deep understanding. As Alexander Pope said, a little learning is a dangerous thing.
- C++: In 24 hours you might be able to learn some of the syntax of C++ (if you already know another language), but you couldn't learn much about how to use the language. In short, if you were, say, a Basic programmer, you could learn to write programs in the style of Basic using C++ syntax, but you couldn't learn what C++ is actually good (and bad) for. So what's the point? Alan Perlis once said: "A language that doesn't affect the way you think about programming, is not worth knowing". One possible point is that you have to learn a tiny bit of C++ (or more likely, something like JavaScript or Processing) because you need to interface with an existing tool to accomplish a specific task. But then you're not learning how to program; you're learning to accomplish that task.
- in 24 Hours: Unfortunately, this is not enough, as the next section shows.
Teach Yourself Programming in Ten Years
Researchers (Bloom (1985), Bryan & Harter (1899), Hayes (1989), Simmon & Chase (1973)) have shown it takes about ten years to develop expertise in any of a wide variety of areas, including chess playing, music composition, telegraph operation, painting, piano playing, swimming, tennis, and research in neuropsychology and topology. The key is deliberative practice: not just doing it again and again, but challenging yourself with a task that is just beyond your current ability, trying it, analyzing your performance while and after doing it, and correcting any mistakes. Then repeat. And repeat again. There appear to be no real shortcuts: even Mozart, who was a musical prodigy at age 4, took 13 more years before he began to produce world-class music. In another genre, the Beatles seemed to burst onto the scene with a string of #1 hits and an appearance on the Ed Sullivan show in 1964. But they had been playing small clubs in Liverpool and Hamburg since 1957, and while they had mass appeal early on, their first great critical success, Sgt. Peppers, was released in 1967.
Malcolm Gladwell has popularized the idea, although he concentrates on 10,000 hours, not 10 years. Henri Cartier-Bresson (1908-2004) had another metric: "Your first 10,000 photographs are your worst." (He didn't anticipate that with digital cameras, some people can reach that mark in a week.) True expertise may take a lifetime: Samuel Johnson (1709-1784) said "Excellence in any department can be attained only by the labor of a lifetime; it is not to be purchased at a lesser price." And Chaucer (1340-1400) complained "the lyf so short, the craft so long to lerne." Hippocrates (c. 400BC) is known for the excerpt "ars longa, vita brevis", which is part of the longer quotation "Ars longa, vita brevis, occasio praeceps, experimentum periculosum, iudicium difficile", which in English renders as "Life is short, [the] craft long, opportunity fleeting, experiment treacherous, judgment difficult." Of course, no single number can be the final answer: it doesn't seem reasonable to assume that all skills (e.g., programming, chess playing, checkers playing, and music playing) could all require exactly the same amount of time to master, nor that all people will take exactly the same amount of time. As Prof. K. Anders Ericssonputs it, "In most domains it's remarkable how much time even the most talented individuals need in order to reach the highest levels of performance. The 10,000 hour number just gives you a sense that we're talking years of 10 to 20 hours a week which those who some people would argue are the most innately talented individuals still need to get to the highest level."
So You Want to be a Programmer
Here's my recipe for programming success:
- Get interested in programming, and do some because it is fun. Make sure that it keeps being enough fun so that you will be willing to put in your ten years/10,000 hours.
- Program. The best kind of learning is learning by doing. To put it more technically, "the maximal level of performance for individuals in a given domain is not attained automatically as a function of extended experience, but the level of performance can be increased even by highly experienced individuals as a result of deliberate efforts to improve." (p. 366) and "the most effective learning requires a well-defined task with an appropriate difficulty level for the particular individual, informative feedback, and opportunities for repetition and corrections of errors." (p. 20-21) The book Cognition in Practice: Mind, Mathematics, and Culture in Everyday Life is an interesting reference for this viewpoint.
- Talk with other programmers; read other programs. This is more important than any book or training course.
- If you want, put in four years at a college (or more at a graduate school). This will give you access to some jobs that require credentials, and it will give you a deeper understanding of the field, but if you don't enjoy school, you can (with some dedication) get similar experience on your own or on the job. In any case, book learning alone won't be enough. "Computer science education cannot make anybody an expert programmer any more than studying brushes and pigment can make somebody an expert painter" says Eric Raymond, author of The New Hacker's Dictionary. One of the best programmers I ever hired had only a High School degree; he's produced a lot of great software, has his own news group, and made enough in stock options to buy his own nightclub.
- Work on projects with other programmers. Be the best programmer on some projects; be the worst on some others. When you're the best, you get to test your abilities to lead a project, and to inspire others with your vision. When you're the worst, you learn what the masters do, and you learn what they don't like to do (because they make you do it for them).
- Work on projects after other programmers. Understand a program written by someone else. See what it takes to understand and fix it when the original programmers are not around. Think about how to design your programs to make it easier for those who will maintain them after you.
- Learn at least a half dozen programming languages. Include one language that emphasizes class abstractions (like Java or C++), one that emphasizes functional abstraction (like Lisp or ML or Haskell), one that supports syntactic abstraction (like Lisp), one that supports declarative specifications (like Prolog or C++ templates), and one that emphasizes parallelism (like Clojure or Go).
- Remember that there is a "computer" in "computer science". Know how long it takes your computer to execute an instruction, fetch a word from memory (with and without a cache miss), read consecutive words from disk, and seek to a new location on disk. (Answers here.)
- Get involved in a language standardization effort. It could be the ANSI C++ committee, or it could be deciding if your local coding style will have 2 or 4 space indentation levels. Either way, you learn about what other people like in a language, how deeply they feel so, and perhaps even a little about why they feel so.
- Have the good sense to get off the language standardization effort as quickly as possible.
With all that in mind, its questionable how far you can get just by book learning. Before my first child was born, I read all the How To books, and still felt like a clueless novice. 30 Months later, when my second child was due, did I go back to the books for a refresher? No. Instead, I relied on my personal experience, which turned out to be far more useful and reassuring to me than the thousands of pages written by experts.
Fred Brooks, in his essay No Silver Bullet identified a three-part plan for finding great software designers:
- Systematically identify top designers as early as possible.
- Assign a career mentor to be responsible for the development of the prospect and carefully keep a career file.
- Provide opportunities for growing designers to interact and stimulate each other.
This assumes that some people already have the qualities necessary for being a great designer; the job is to properly coax them along. Alan Perlis put it more succinctly: "Everyone can be taught to sculpt: Michelangelo would have had to be taught how not to. So it is with the great programmers". Perlis is saying that the greats have some internal quality that transcends their training. But where does the quality come from? Is it innate? Or do they develop it through diligence? As Auguste Gusteau (the fictional chef inRatatouille) puts it, "anyone can cook, but only the fearless can be great." I think of it more as willingness to devote a large portion of one's life to deliberative practice. But maybe fearless is a way to summarize that. Or, as Gusteau's critic, Anton Ego, says: "Not everyone can become a great artist, but a great artist can come from anywhere."
So go ahead and buy that Java/Ruby/Javascript/PHP book; you'll probably get some use out of it. But you won't change your life, or your real overall expertise as a programmer in 24 hours or 21 days. How about working hard to continually improve over 24 months? Well, now you're starting to get somewhere...
References
Bloom, Benjamin (ed.) Developing Talent in Young People, Ballantine, 1985.
Brooks, Fred, No Silver Bullets, IEEE Computer, vol. 20, no. 4, 1987, p. 10-19.
Hayes, John R., Complete Problem Solver Lawrence Erlbaum, 1989.
Chase, William G. & Simon, Herbert A. "Perception in Chess" Cognitive Psychology, 1973, 4, 55-81.
Lave, Jean, Cognition in Practice: Mind, Mathematics, and Culture in Everyday Life, Cambridge University Press, 1988.
Answers
Approximate timing for various operations on a typical PC:
| execute typical instruction | 1/1,000,000,000 sec = 1 nanosec |
| fetch from L1 cache memory | 0.5 nanosec |
| branch misprediction | 5 nanosec |
| fetch from L2 cache memory | 7 nanosec |
| Mutex lock/unlock | 25 nanosec |
| fetch from main memory | 100 nanosec |
| send 2K bytes over 1Gbps network | 20,000 nanosec |
| read 1MB sequentially from memory | 250,000 nanosec |
| fetch from new disk location (seek) | 8,000,000 nanosec |
| read 1MB sequentially from disk | 20,000,000 nanosec |
| send packet US to Europe and back | 150 milliseconds = 150,000,000 nanosec |
Appendix: Language Choice
Several people have asked what programming language they should learn first. There is no one answer, but consider these points:
- Use your friends. When asked "what operating system should I use, Windows, Unix, or Mac?", my answer is usually: "use whatever your friends use." The advantage you get from learning from your friends will offset any intrinsic difference between OS, or between programming languages. Also consider your future friends: the community of programmers that you will be a part of if you continue. Does your chosen language have a large growing community or a small dying one? Are there books, web sites, and online forums to get answers from? Do you like the people in those forums?
- Keep it simple. Programming languages such as C++ and Java are designed for professional development by large teams of experienced programmers who are concerned about the run-time efficiency of their code. As a result, these languages have complicated parts designed for these circumstances. You're concerned with learning to program. You don't need that complication. You want a language that was designed to be easy to learn and remember by a single new programmer.
- Play. Which way would you rather learn to play the piano: the normal, interactive way, in which you hear each note as soon as you hit a key, or "batch" mode, in which you only hear the notes after you finish a whole song? Clearly, interactive mode makes learning easier for the piano, and also for programming. Insist on a language with an interactive mode and use it.
Given these criteria, my recommendations for a first programming language would be Python or Scheme. Another choice is Javascript, not because it is perfectly well-designed for beginners, but because there are so many online tutorials for it, such as Khan Academy's tutorial. But your circumstances may vary, and there are other good choices. If your age is a single-digit, you might prefer Alice or Squeak or Blockly (older learners might also enjoy these). The important thing is that you choose and get started.
Appendix: Books and Other Resources
Several people have asked what books and web pages they should learn from. I repeat that "book learning alone won't be enough" but I can recommend the following:
- Scheme: Structure and Interpretation of Computer Programs (Abelson & Sussman) is probably the best introduction to computer science, and it does teach programming as a way of understanding the computer science. You can see online videos of lectures on this book, as well as the complete text online. The book is challenging and will weed out some people who perhaps could be successful with another approach.
- Scheme: How to Design Programs (Felleisen et al.) is one of the best books on how to actually design programs in an elegant and functional way.
- Python: Python Programming: An Intro to CS (Zelle) is a good introduction using Python.
- Python: Several online tutorials are available at Python.org.
- Oz: Concepts, Techniques, and Models of Computer Programming (Van Roy & Haridi) is seen by some as the modern-day successor to Abelson & Sussman. It is a tour through the big ideas of programming, covering a wider range than Abelson & Sussman while being perhaps easier to read and follow. It uses a language, Oz, that is not widely known but serves as a basis for learning other languages. <
Notes
T. Capey points out that the Complete Problem Solver page on Amazon now has the "Teach Yourself Bengali in 21 days" and "Teach Yourself Grammar and Style" books under the "Customers who shopped for this item also shopped for these items" section. I guess that a large portion of the people who look at that book are coming from this page. Thanks to Ross Cohen for help with Hippocrates.