用十年来学编程_中英对照.doc

Teach Yourself Programming in Ten YearsPeter NorvigWhy is everyone in such a rush?Walk into any bookstore, and youll see how to Teach Yourself Java in 7 Days alongside endless variations offering to teach Visual Basic, Windows, the Internet, and so on in a few days or hours. I did the following power search at A: pubdate: after 1992 and title: days and (title: learn or title: teach yourself)and got back 248 hits. The first 78 were computer books (number 79 was Learn Bengali in 30 days). I replaced days with hours and got remarkably similar results: 253 more books, with 77 computer books followed by Teach Yourself Grammar and Style in 24 Hours at number 78. Out of the top 200 total, 96% were computer books. The conclusion is that either people are in a big rush to learn about computers, or that computers are somehow fabulously easier to learn than anything else. There are no books on how to learn Beethoven, or Quantum Physics, or even Dog Grooming in a few days. 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. Lets analyze what a title like Learn C+ in Three Days could mean: Learn: In 3 days you wont have time to write several significant programs, and learn from your successes and failures with them. You wont have time to work with an experienced programmer and understand what it is like to live in a C+ environment. In short, you wont 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 3 days you might be able to learn some of the syntax of C+ (if you already know another language), but you couldnt 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 couldnt learn what C+ is actually good (and bad) for. So whats the point? Alan Perlis once said: A language that doesnt 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 Flashs Flex) because you need to interface with an existing tool to accomplish a specific task. But then youre not learning how to program; youre learning to accomplish that task. in Three Days: Unfortunately, this is not enough, as the next section shows. Teach Yourself Programming in Ten YearsResearchers (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 reports that a study of students at the Berlin Academy of Music compared the top, middle, and bottom third of the class and asked them how much they had practiced: Everyone, from all three groups, started playing at roughly the same time - around the age of five. In those first few years, everyone practised roughly the same amount - about two or three hours a week. But around the age of eight real differences started to emerge. The students who would end up as the best in their class began to practise more than everyone else: six hours a week by age nine, eight by age 12, 16 a week by age 14, and up and up, until by the age of 20 they were practising well over 30 hours a week. By the age of 20, the elite performers had all totalled 10,000 hours of practice over the course of their lives. The merely good students had totalled, by contrast, 8,000 hours, and the future music teachers just over 4,000 hours. So it may be that 10,000 hours, not 10 years, is the magic number. (Henri Cartier-Bresson (1908-2004) said Your first 10,000 photographs are your worst, but he shot more than one an hour.) Samuel Johnson (1709-1784) thought it took even longer: 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. Although in Latin, ars can mean either art or craft, in the original Greek the word techne can only mean skill, not art. Heres 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 ten years. Talk to other programmers; read other programs. This is more important than any book or training course. 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. 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 dont enjoy school, you can (with some dedication) get similar experience on the job. In any case, book learning alone wont 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 Hackers Dictionary. One of the best programmers I ever hired had only a High School degree; hes 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 youre the best, you get to test your abilities to lead a project, and to inspire others with your vision. When youre the worst, you learn what the masters do, and you learn what they dont like to do (because they make you do it for them). Work on projects after other programmers. Be involved in understanding 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 it after you. Learn at least a half dozen programming languages. Include one language that supports class abstractions (like Java or C+), one that supports functional abstraction (like Lisp or ML), one that supports syntactic abstraction (like Lisp), one that supports declarative specifications (like Prolog or C+ templates), one that supports coroutines (like Icon or Scheme), and one that supports parallelism (like Sisal). 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: 1. Systematically identify top designers as early as possible. 2. Assign a career mentor to be responsible for the development of the prospect and carefully keep a career file. 3. 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. So go ahead and buy that Java book; youll probably get some use out of it. But you wont change your life, or your real overall expertise as a programmer in 24 hours, days, or even months. 用十年来学编程Peter Norvig为什么每个人都急不可耐？走进任何一家书店，你会看见Teach Yourself Java in 7 Days（7天Java无师自通）的旁边是一长排看不到尽头的类似书籍，它们要教会你Visual Basic、Windows、Internet等等，而只需要几天甚至几小时。我在A上进行了如下搜索：pubdate: after 1992 and title: days and (title: learn or title: teach yourself)(出版日期：1992年后 and 书名：天 and （书名：学会 or 书名：无师自通）)我一共得到了248个搜索结果。前面的78个是计算机书籍（第79个是Learn Bengali in 30 days，30天学会孟加拉语）。我把关键词“days”换成“hours”，得到了非常相似的结果：这次有253本书，头77本是计算机书籍，第78本是Teach Yourself Grammar and Style in 24 Hours（24小时学会文法和文体）。头200本书中，有96%是计算机书籍。结论是，要么是人们非常急于学会计算机，要么就是不知道为什么计算机惊人地简单，比任何东西都容易学会。没有一本书是要在几天里教会人们欣赏贝多芬或者量子物理学，甚至怎样给狗打扮。在How to Design Programs这本书里说“Bad programming is easy. Idiots can learn it in 21 days, even if they are dummies.” （坏的程序是很容易的，就算他们是笨蛋白痴都可以在21天内学会。）让我们来分析一下像Learn C+ in Three Days（3天学会C+）这样的题目到底是什么意思： 学会：在3天时间里，你不够时间写一些有意义的程序，并从它们的失败与成功中学习。你不够时间跟一些有经验的程序员一起工作，你不会知道在C+那样的环境中是什么滋味。简而言之，没有足够的时间让你学到很多东西。所以这些书谈论的只是表面上的精通，而非深入的理解。如Alexander Pope（英国诗人、作家，1688-1744）所言，一知半解是危险的（a little learning is a dangerous thing） C+：在3天时间里你可以学会C+的语法（如果你已经会一门类似的语言），但你无法学到多少如何运用这些语法。简而言之，如果你是，比如说一个Basic程序员，你可以学会用C+语法写出Basic风格的程序，但你学不到C+真正的优点（和缺点）。那关键在哪里？Alan Perlis（ACM第一任主席，图灵奖得主，1922-1990）曾经说过：“如果一门语言不能影响你对编程的想法，那它就不值得去学”。另一种观点是，有时候你不得不学一点C+（更可能是JavaScript和Flash Flex之类）的皮毛，因为你需要接触现有的工具，用来完成特定的任务。但此时你不是在学习如何编程，你是在学习如何完成任务。 3天：不幸的是，这是不够的，正如下一节所言。 10年学编程一些研究者（Bloom (1985), Bryan & Harter (1899), Hayes (1989), Simmon & Chase (1973)）的研究表明，在许多领域，都需要大约10 年时间才能培养出专业技能，包括国际象棋、作曲、绘画、钢琴、游泳、网球，以及神经心理学和拓扑学的研究。似乎并不存在真正的捷径：即使是莫扎特，他4 岁就显露出音乐天才，在他写出世界级的音乐之前仍然用了超过13年时间。再看另一种音乐类型的披头士，他们似乎是在1964年的Ed Sullivan节目中突然冒头的。但其实他们从1957年就开始表演了，即使他们很早就显示出了巨大的吸引力，他们第一次真正的成功Sgt. Peppers也要到1967年才发行。Malcolm Gladwell 研究报告称，把在伯林音乐学院学生一个班的学生按水平分成高中低，然后问他们对音乐练习花了多少工夫：在这三个小组中的每一个人基本上都是从相同的时间开始练习的（在五岁的时候）。在开始的几年里，每个人都是每周练习2-3个小时。但是在八岁的时候，练习的强度开始显现差异。在这个班中水平最牛的人开始比别人练习得更多在九岁的时候每周练习6个小时，十二岁的时候，每周8个小时，十四岁的时候每周16个小时，并在成长过程中练习得越来越多，到20岁的时候，其每周练习可超过30个小时。到了20岁，这些优秀者在其生命中练习音乐总共超过 10,000 小时。与之对比，其它人只平均有8,000小时，而未来只能留校当老师的人仅仅是4,000 小时。所以，这也许需要10,000 小时，并不是十年，但这是一个magic number。Samuel Johnson（英国诗人）认为10 年还是不够的：“任何领域的卓越成就都只能通过一生的努力来获得；稍低一点的代价也换不来。”（Excellence in any department can be attained only by the labor of a lifetime; it is not to be purchased at a lesser price.） 乔叟（Chaucer，英国诗人，1340-1400）也抱怨说：“生命如此短暂，掌握技艺却要如此长久。”（the lyf so short, the craft so long to lerne.）下面是我在编程这个行当里获得成功的处方： 对编程感兴趣，因为乐趣而去编程。确定始终都能保持足够的乐趣，以致你能够将10年时间投入其中。 跟其他程序员交谈；阅读其他程序。这比任何书籍或训练课程都更重要。 编程。最好的学习是从实践中学习。用更加技术性的语言来讲，“个体在特定领域最高水平的表现不是作为长期的经验的结果而自动获得的，但即使是非常富有经验的个体也可以通过刻意的努力而提高其表现水平。”（p. 366），而且“最有效的学习要求为特定个体制定适当难度的任务，有意义的反馈，以及重复及改正错误的机会。”（p. 20-21）Cognition in Practice: Mind, Mathematics, and Culture in Everyday Life（在实践中认知：心智、数学和日常生活的文化）是关于这个观点的一本有趣的参考书。 如果你愿意，在大学里花上4年时间（或者再花几年读研究生）。这能让你获得一些工作的入门资格，还能让你对此领域有更深入的理解，但如果你不喜欢进学校，（作出一点牺牲）你在工作中也同样能获得类似的经验。在任何情况下，单从书本上学习都是不够的。“计算机科学的教育不会让任何人成为内行的程序员，正如研究画笔和颜料不会让任何人成为内行的画家”, Eric Raymond，The New Hackers Dictionary（新黑客字典）的作者如是说。我曾经雇用过的最优秀的程序员之一仅有高中学历；但他创造出了许多伟大的软件（XEmacs, Mozilla），甚至有讨论他本人的新闻组，而且股票期权让他达到我无法企及的富有程度（译注：指Jamie Zawinski，Xemacs和Netscape的作者）。 跟别的程序员一起完成项目。在一些项目中成为最好的程序员；在其他一些项目中当最差的一个。当你是最好的程序员时，你要测试自己领导项目的能力，并通过你的洞见鼓舞其他人。当你是最差的时候，你学习高手们在做些什么，以及他们不喜欢做什么（因为他们让你帮他们做那些事）。 接手别的程序员完成项目。用心理解别人编写的程序。看看在没有最初的程序员在场的时候理解和修改程序需要些什么。想一想怎样设计你的程序才能让别人接手维护你的程序时更容易一些。 学会至少半打编程语言。包括一门支持类抽象（class abstraction）的语言（如Java或C+），一门支持函数抽象（functional abstraction）的语言（如Lisp或ML），一门支持句法抽象（syntactic abstraction）的语言（如Lisp），一门支持说明性规约（declarative specification）的语言（如Prolog或C+模版），一门支持协程（coroutine）的语言（如Icon或Scheme），以及一门支持并行处理（parallelism）的语言（如Sisal）。 记住在“计算机科学”这个词组里包含“计算机”这个词。了解你的计算机执行一条指令要多长时间，从内存中取一个word要多长时间（包括缓存命中和未命中的情况），从磁盘上读取连续的数据要多长时间，定位到磁盘上的新位置又要多长时间。（答案answers在这里） 尝试参与到一项语言标准化工作中。可以是ANSI C+委员会，也可以是决定自己团队的编码风格到底采用2个空格的缩进还是4个。不论是哪一种，你都可以学到在这门语言中到底人们喜欢些什么，他们有多喜欢，甚至有可能稍微了解为什么他们会有这样的感觉。 拥有尽快从语言标准化工作中抽身的良好判断力。 抱着这些想法，我很怀疑从书上到底能学到多少东西。在我第一个孩子出生前，我读完了所有“怎样”的书，却仍然感到自己是个茫无头绪的新手。30个月后，我第二个孩子出生的时候，我重新拿起那些书来复习了吗？不。相反，我依靠我自己的经验，结果比专家写的几千页东西更有用更靠得住。Fred Brooks在他的短文No Silver Bullets（没有银弹）中确立了如何发现杰出的软件设计者的三步规划： 尽早系统地识别出最好的设计者群体。 指派一个事业上的导师负责有潜质的对象的发展，小心地帮他保持职业生涯的履历。 让成长中的设计师们有机会互相影响，互相激励。 这实际上是假定了有些人本身就具有成为杰出设计师的必要潜质；要做的只是引导他们前进。Alan Perlis说得更简洁：“每个人都可以被教授如何雕塑；而对米开朗基罗来说，能教给他的倒是怎样能够不去雕塑。杰出的程序员也一样”。所以尽管去买那些Java书；你很可能会从中找到些用处。但你的生活，或者你作为程序员的真正的专业技术，并不会因此在24小时、24天甚至24个月内发生真正的变化。ReferencesBloom, 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. AnswersApproximate 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 ChoiceSeveral 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. Youre concerned with learning to program. You dont 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. But your circumstances may vary, and there are other good choices. If your age is a single-digit, you might prefer Alice or Squeak (older learners might also enjoy these). The important thing is that you choose and get started. Appendix: Books and Other Resources