Peter Norvig：十年学会编程

出处：http://norvig.com/21-days.html

为啥都想速成？

随便逛一下书店，你会看到《7天自学Java》等诸如此类的N天甚至N小时学习Visual Basic、Windows、Internet的书。我用亚马逊网站的搜索功能，出版年份选1992年以后，书名关键词是：“天”、“自学”、“教你”，查到248个结果，前78个是计算机类图书，第79个是《30天学孟加拉语》。我用“天”换成“小时”，结果更惊人，有多达253本书，前77本是计算机图书，第78是《24小时自学语法句式》。在前200名中，96%是计算机的书。

结论就是：要么人们急于学习电脑，要么计算机比其他东西学起来要异常简单。没有任何书是关于几天学习贝多芬或量子物理的，甚至连犬类装扮都没有。费雷森（Felleisen）等人在其著作《如何设计程序》中同意这个趋势，其中提到：“坏设计很简单，笨蛋才用21天学，尽管他们还是真傻。”

让我们看看《三日学会C++》这个书名意味着什么：

◇学习：
三天内你可能没有时间写出有意义的程序，或者从中积累经验。你不可能有时间去跟职业编程者一起去理解在C++环境下的状况。简而言之，你没有充足的时间学很多。所以这本书只能说肤浅的知识。正如亚历山大·波普（Alexander Pope）所言：一知半解是很危险的。

◇C++：
三天内你可能学会C++的句法（如果你已经了解其他的语言），但你还不会使用它。打个比方，假如你是个Basic程序员，你可能写出Basic风格的C++程序，而无法理解C++的真实好处。那要点是什么？艾伦·佩里斯(Alan Perlis)曾经说过：“一门不能影响你编程观点的语言不足学的。”有可能你学了一点点C++（或者诸如Javascript、Flex之类），因为你需要和现成的工具接口以完成手头的任务。这种情况下，你不是在学习如何编程，只是在学习如何完成任务。

◇三日：
不幸地是，这远远不够，下一部分会详细讲。

如何用十年掌握编程

研究人员（Bloom (1985), Bryan & Harter (1899), Hayes (1989), Simmon & Chase (1973)）得出结论：想要在诸多领域达到职业水平需要十年，比如国际象棋，作曲，电报操作，绘画，弹钢琴，游泳，网球以及神经心理学和拓扑学的研究。关键是精心练习，只是一遍一遍地重复是不够的，必须挑战恰好超越你能限的事情，尝试并思考你的表现，并自我矫正。周而复始。这并无捷径！4岁的音乐奇才莫扎特用了13年才能创作世界级的音乐。另外，披头士乐队似乎在1964年的埃德·苏利文（ Ed Sullivan show）演出中一炮而红，但是他们自从1957年就在利物浦和汉堡的酒吧演出，在取得广泛关注后，第一部重量级作品《佩珀军士》（Sgt. Peppers）是在1967年发行。马尔科姆·格拉德威尔（Malcolm Gladwell）撰文描述了一项针对柏林音乐学院学生的研究，他们被分为尖子，中等和不足三类，并被问到他们练琴的情况：
所有三组中的人，开始学琴的年龄大概相差无几，五岁左右。在刚开始的几年，所有人练习量也差不多，一周两三个小时。自八岁开始，实质性变化就有了。那些精英学生开始比其他人练习更多：九岁的时候一周六个小时，十二岁的时候一周八个小时，十四岁的时候一周十六个小时，一直到二十岁的时候一周要超过三十小时。截止到二十岁，在他们的生涯里已经有总计一万小时练琴。仅仅表现可以的那部分学生加起来是八千小时，那些未来的音乐老师有四千小时。

所以，更确切地说，一万小时，而非十年，是个神奇之数。萨缪尔·约翰逊（Samuel Johnson, 1709-1784）认为还需更长时间：“卓越乃一生之追求，而非其它”。 乔叟（Chaucer, 1340-1400）抱怨道"the lyf so short, the craft so long to lerne." （生之有限，学也无涯）。希波克拉底（Hippocrates, c. 400BC）因这句话被世人所知："ars longa, vita brevis"（译注：拉丁语，意为“艺无尽，生有涯”），更长的版本是 "Ars longa, vita brevis, occasio praeceps, experimentum periculosum, iudicium difficile"，翻译成英文就是 "Life is short, (the) craft long, opportunity fleeting, experiment treacherous, judgment difficult." （生有涯，艺无尽，机遇瞬逝，践行误导，决断不易）。

我的编程成功秘笈是：

◇首先要对编程感兴趣，能从编程中得到乐趣。一定要让它足够有趣，因为你要保持你的兴趣长达十年。

◇与别的程序员交流；阅读别人的代码——这比看任何书或参加培训课都重要。

◇实践。最好的学习乃实践。俗话说：“编程的至高境界一定要通过充分的实践才能达到，而个人的能力可通过不懈努力获得显著提升。” (p. 366) “最有效率的学习需要明确的目标，适当的难度，知识回馈，并容许重复或修正错误。” (p. 20-21) 《实践认知：每日的思维、数学及文化》（Cognition in Practice: Mind, Mathematics, and Culture in Everyday Life） 在这方面可做参考。

◇如果你愿意，花四年学习大学课程（或者再加上读研）。这将给你赢得某些工作机会，并给予你在该领域的深层见解。但如果你不喜欢学校的学习，你同样可以在工作中获得相似的经验。无论如何，单靠书本是远远不够的。“学习计算机科学不会让你成为编程专家，如同学习绘画和色彩理论不会让你成为画家一样”。这是埃里克·雷蒙德（Eric Raymond）说的，他是《新黑客字典》（The New Hacker's Dictionary）的作者。我雇用过的最优秀程序员，只有高中文凭。但他开发过许多伟大软件，有自己的新闻组，通过公司认股赚的钱就让他买下了自己的夜店。

◇和其他程序员一起参与工程项目。在某些项目中担当最优秀程序员，在另一些项目中充当最差劲程序员。充当领头羊的时候，你要测试你领导一项工程的能力，并用你的视野来激发他人；如果在项目组中垫底，就应该学习其它牛人在做些啥，以及他们不喜欢做的（看他们把哪些活让给你做）。

◇继续别人的工程项目。去理解先前程序员写的程序。学习如何理解并解决先前程序员没有考虑到的问题。思考你的程序该如何设计以便让之后的程序员更容易维护。

◇至少学6种程序语言。其中包括一种支持类抽象的（Java和C++），一种支持函数抽象的（如Lisp或ML），一种支持语义抽象的（Lisp），一种支援声明规范的（如Prolog或C++模板），还有一种支援协程的（Icon或Scheme），另外一种支持并发的（Sisal）。

◇记住，在“计算机科学”里有“计算机”一词。理解计算机执行你的代码的时候花费的时间。比如：从内存中取一个字（考虑有无缓存未命中情形），连续从磁盘读字，或者在磁盘中定位。

◇参加语言标准化工作。这可能是有关 ANSI C++ 委员会，也可能是决定你编码风格是两格缩进或四格缩进。无论如何，你要知道其他人对语言的喜好程度，有时还要想想他们为什么喜欢这样。

◇知道自己应该在何时脱身于语言标准化

所有上述这些，很难通过书本的学习来达到。我头一个孩子出生时，我读了所有的“如何做”（How To）系列的书籍，却依然对育婴毫无头绪。30个月后，我第二个孩子出生，我还需要温习一下那些书吗？绝对不！相反，我完全可以参照个人经验，而结果相当有效。这更让我确信：我的经验胜过那些专家们写的上千页文字。

弗雷德·布鲁克斯（Fred Brooks）在《没有银弹》（No Silver Bullet）一书给出了寻找顶级设计师的三条建议：
◇尽早系统地识别出顶级设计师。
◇分配一个人作为其职业规划的导师。
◇给予机遇让成长中的设计师互相磨砺。

此处假定有部分人已经有成为伟大设计师的潜质，你所需的就是要诱导他们。艾伦·佩里斯（Alan Perlis）一针见血地指出："假如人人都可以学雕刻，那就得教米开朗基罗如何不去干雕刻。对于伟大程序员，也是如此。”

所以，简单地买一本Java书，你或许能找到些有用的东西，但绝不会让你在24小时内甚至24天抑或24月内，成为行家里手。

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. Bryan, W.L. & Harter, N. "Studies on the telegraphic language: The acquisition of a hierarchy of habits. Psychology Review, 1899, 8, 345-375 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.