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十年学会编程
著者： Peter Norvig
翻译： Dai Yuwen
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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，还有各种各样的
变体：在几天内或几小时内学会Visual Basic, Windows, Internet等等，等等。我在Am
azon 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。Sam
uel Johnson 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 coroutine的语言（象Icon或Sch
eme），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）
使自己卷入一种语言标准化的工作里。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：假如米开朗其罗被教成如
何不会雕刻。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
Peter Norvig (Copyright 2001)
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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.
Let's analyze what a title like Learn Pascal 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 that environment. In short, you won't
have time to learn much. So
they can only be talking about a superficial familiarity, not a deep
understanding. As Alexander Pope
said, a little learning is a dangerous thing.
Pascal: In 3 days you might be able to learn the syntax of Pascal (if you
already knew a similar
language), but you couldn't learn much about how to use the syntax. In
short, if you were, say, a Basic
programmer, you could learn to write programs in the style of Basic using
Pascal syntax, but you
couldn't learn what Pascal 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 Pascal (or more
likely, something like Visual
Basic or javascript) 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 (Hayes, Bloom) have shown it takes about ten years to develop
expertise in any of a wide
variety of areas, including chess playing, music composition, painting,
piano playing, swimming,
tennis, and research in neuropsychology and topology. 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,
appearing on the Ed Sullivan show
in 1964. But they had been playing since 1957, and while they had mass
appeal early on, their first
great critical success, Sgt. Peppers, was released in 1967. Samuel Johnson
thought it took longer than
ten years: "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 complained "the lyf so short,
the craft so long to lerne."
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 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 don't enjoy school, you can (with some dedication) get similar
experience 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 through stock
options is no doubt much richer than I'll ever be.
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. 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 Bullets 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".
So go ahead and buy that Java 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 months.
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.
Lave, Jean, Cognition in Practice: Mind, Mathematics, and Culture in
Everyday Life, Cambridge
University Press, 1988.
http://www.norvig.com/
Peter Norvig
Google
2400 Bayshore Parkway
Mountain View, CA 94043 Email: peter@norvig.com
Phone: 650-623-4248
Fax: 650-618-1499
Web: norvig.com
Note to recruiters: Please don't offer me a job. I already have the best
job in the world at the best
company in the world.
Note to engineers, researchers, managers: see why you should apply to help.
Professional Employment (Full-Time)
2001-now Google Director of Search Quality
1998-2001 NASA Ames Research Center Division Chief, Computational Sciences
1996-1998 Junglee Corp. Chief Scientist
1994-1996 Harlequin, Inc. Chief Designer
1991-1994 Sun Microsystems Labs Senior Scientist
1986-1991 University of California, Berkeley Research Faculty Member
1985-1986 University of Southern California Assistant Professor
1978-1980 Higher Order Software, Inc. Member of Technical Staff
1977-1977 Woods Hole Oceanographic Institute Summer Programming Intern
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十年学会编程