by: http://www.norvig.com/21-days.html
Why is everyone in such a rush?
Walk into any bookstore, and you'll 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 Amazon.com: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.Let's analyze what a title like Learn C++ in Three Days could mean:
- Learn: In 3 days 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 3 days 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 Flash's Flex) 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 Three Days: 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 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".
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 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.
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.
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, days, or even weeks. 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.
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.
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翻譯內文
為何人人都如此匆忙？
走進任何一家書店，你會看到如《７天自學爪哇語言》這類的書，擺了長長一排幾乎
看不到盡頭。這些並排的書還有視窗作業系統、網際網路、視覺化培基語言等。有些甚至
強調只要幾天甚至幾個小時。我在亞馬遜網路書店，以下列關鍵字，進行條件交叉的強力
搜尋：
出版年限：１９９２以後 且 書名：天數 且 書名：學習 或 書名：自學
我找到了２４８個條件相符的結果。前７８個是電腦書（排第７９的是《３０天學會
孟加拉語》）。我把關鍵詞『天數』換成了『小時』，得到近似的結果；這次有２５３本
，前７７本是電腦書籍，第７８本是《２４小時自學文法與風格》。排名前２００本書中
，有９６％是電腦書籍。
我得到的結論是，人們要不是急著想學會電腦，就是電腦太簡單了，比其他事物都要
容易學得會。沒有一本書是要在幾天�，就教會如何欣賞貝多芬或量子物理學，甚至是幫
狗兒打扮。
讓我們分析像《三天學會巴斯卡語言》這樣書名想傳達什麼意旨：
◎學會
在三天內，你沒有時間去寫幾支有意義的程式，並從其中領略對與錯。你也沒時間跟
有經驗的程式師一塊兒工作，所以你無法瞭解在那種環境下的實際情形。簡單來說，就學
習而言，時間根本不夠用。所以這些書只能談談表面的『精通』，而不是深度的認知。如
同亞歷山大˙蒲柏所言：「一知半解是件危險的事。」
◎巴斯卡語言
三天內你或可學會巴斯卡語言的語法（如果你已會一個類似的電腦語言），但你無法
學會如何妥善運用。簡言之，如果你是個培基語言程式師，你可以用巴斯卡語言寫出類似
培基語言風格的程式，但你學不到巴斯卡語言的優點（還有缺點）。那麼重點宄竟是什麼
？艾倫˙柏立士曾說：「如果電腦語言不能影響你寫程式時的思維，那就不值得去學。」
另一個可能的觀點是，你必須學會一點點巴斯卡語言（或是像視覺化培基語言、爪哇
描述語言），因為你需要跟現成的工具配合，用它來完成特定的工作。不過這個時候，你
可不是在學怎麼寫程式，而是要學會完成工作。
◎三天
很不幸，這根本不夠；在下節我會告訴你的。
十年自學程式設計
研究學者（海斯、布盧姆）的研究說明，在許多領域，大約十年才能培養出專業技能
；包括下西洋棋、作曲、繪畫、鋼琴演奏、游泳、網球，及神經心理學和數學拓撲的研究
。似乎沒有真正的捷徑；即便是莫扎特在四歲就展露出音樂天才，在他寫出世界級的音樂
之前仍然用了超過十三年的時間。
再看另一種類型的代表，披頭四樂團，他們似乎是在１９６４年的艾德˙蘇利文劇場
表演，突然地成為熱門樂團首席。其實他們從１９５７年開始，就在利物浦、漢堡等地的
小型俱樂部表演了。雖然他們很早就顯現強大的吸引力，但他們具決定性的成功作品《胡
椒中士》也要到１９６７年才首次發行。山姆爾˙強森則認為十年根本不夠：「任何領域
的卓越成就，只能用一生的努力才能取得；稍微低一點的代價是換不到的。」喬瑟抱怨說
：「生命如此短促，學習技藝卻要這麼地長。」
以下是我在程式設計這個領域獲致成功的秘訣：
˙對程式設計感興趣，因為樂趣而寫程式。確信你自始至終都能樂在其中，這樣你才願意
將十年光陰投入。
◎與其他程式師交流；閱讀其他人的程式。這比任何書、任何訓練課程都來得重要。
◎不斷地寫程式。最好的學習方式是做中學。更專業地說，「在特定領域的個人最高績效
，並不是經驗夠久就會從天下掉下來；但若個人極具經驗，那麼可以透過有計劃的努力來
改進並提昇這種層次的績效。」（第３６６頁）
而「最有效的學習需要，定義明確的任務，特定人則有其相應難度，能增進知識的回
饋，還有重複及修正錯誤的機會。」（第２０∼２１頁）《實踐中認知：心智、數學與日
常生活的文化》是這個觀點的一本有趣參考書籍。
◎如果你想，你可以去讀四年大學（或再讀研究所）。這是你找工作時所需的資格，同時
也可讓你對這個領域有更深的認識。但如你不喜歡學校，你還是可以（得有犧牲）透過工
作獲得類似的經驗。就任何情況來說，只從書本上學是不夠的。「電腦科學的教育無法讓
人成為程式設計的專家，正如研究畫筆跟顏料，也不會讓人成為專業畫家。」艾瑞克˙雷
蒙，《新駭客辭典》的作者這麼說。
我曾聘請最優秀的程式師之一，他只有高中畢業；但他寫出一堆很棒的軟體，還有他
自己的新聞群組。毫無疑問的，股票選擇權讓他變得富有，他的財力令我難以企及。
◎跟其他的程式師一起完成專案。在某些專案成為最佳的程式師；在某些專案中則變成最
差的一個。當你是最佳的，你要測試自己領導專案的能力，並以你的真知灼見鼓勵他人。
當你是最差的，你要學的是，高手做些什麼，還有他們不喜歡做什麼。（因為他們會叫你
去幫他們做。）
◎接手別的程式師完成專案。全心投入並理解別人所寫的程式。當原作者已不在，看看在
理解與修改時有什麼要注意的。想想如何設計程式，能讓後來維護的人容易上手。
◎至少學會五、六種程式語言。其中一種要支援類別抽象的語言（如Ｊａｖａ或Ｃ＋＋）
，一種支援函數抽象（如Ｌｉｓｐ或ＭＬ），一種支援語法抽象（如Ｌｉｓｐ），一種支
援宣告規格（如Ｐｒｏｌｏｇ或Ｃ＋＋樣板），一種支援並行常式（如Ｉｃｏｎ或
Ｓｃｈｅｍｅ），還有一種支援並行處理（如Ｓｉｓａｌ）。
◎記住在『電腦科學』中包括電腦這個詞。要知道你的電腦執行一條指令需時多久，到記
憶體中取一個字組需時多久（快取內有無資料的情形），到磁碟機讀取邏輯相連的字組需
時多久，而磁碟的定位又需要多久。解答在此。
◎參加語言標準化的工作。可以像是ＡＮＳＩ Ｃ＋＋委員會，或由你自己的團隊，來決
定你們的編碼風格，譬如說縮排是２或４個空格。兩者選一，你都能學到別人到底喜歡什
麼，感受有多深，又或許只是稍微瞭解到他們為什麼有這樣的感覺。
◎儘快從語言標準化工作中抽離，並具備良好的判斷力。
自從有了這些想法，我不禁要問究竟能從書上學到多少。在第一個孩子出生前，我讀
完了所有的『怎樣…』的書，仍覺得自己是個一無所知的生手。３０個月後，第二個孩子
出世，我要重回這些書當個好的複習生嗎？不！相反的，我憑著自己的經驗，重拾自信；
這些個人難得的經驗，比專家寫的幾千頁手冊還要有用。
佛雷德瑞克˙布魯克在他的論說文《沒有銀子彈》中指出，發掘卓越軟體設計者的三
部曲：
１．儘早儘可能地，以系統化的方式，發掘最佳設計人員。
２．指派生涯規劃師負責有潛力者的發展，並謹慎地維繫他的生涯規劃。
３．提供機會，讓設計者能相互影響，彼此激勵，藉以成長。
這是假定某些人已具備成為卓越設計師的必要潛能；要做的工作只是誘導他們前進。
艾倫˙柏立士說得更簡潔了。「你可以教任何人學雕塑，但對米開朗基羅而言，要教他的
反倒是有那些事不要做。卓越的程式師也一樣。」
Ｊａｖａ那些書儘管買吧！你或許能從中找到點兒用處。在未來可預見的日子�，或
許是２４小時，幾天，甚至是幾個月吧！你都毋需改變你的生活，或做為一個真正的程式
師應該具備的全能本領。
參考書目
１．Bloom, Benjamin (ed.) Developing Talent in Young People, Ballantine, 1985.
２．Brooks, Fred, No Silver Bullets, IEEE Computer, vol. 20, no. 4, 1987, p. 10-19.
３．Hayes, John R., Complete Problem Solver Lawrence Erlbaum, 1989.
４．Lave, Jean, Cognition in Practice: Mind, Mathematics, and Culture in Everyday Life, Cambridge University Press, 1988.
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