为什么这个函数的名字是reduce？

我的英语不好，我理解的reduce是减少的意思。但这个函数实现的功能我感觉和减少就没有关系。所以请教该怎样理解reduce？

回复内容：

reduce翻译成规约，意思其他答案里面已经讲了。
实际上函数名不应取reduce，应该叫fold，而且要区分foldl和foldr左右两个版本。并行计算里面的那个reduce有个隐含前提，是reduce over monoid，所以结果才与reduce方向无关，可以做有效的并行化。 归约
这是一个函数式编程里面，高阶函数里面很基础的概念。不过我最早听到这个词是在并行计算里面。
函数式编程里面有时也称作 fold ，也就是折叠，这个更好理解吧。详情可参见wikipedia，里面提到了 In functional programming, fold – also known variously as reduce, accumulate, aggregate, compress, or inject
你找一个你觉得好理解的词就OK了。 这就是MapReduce中的reduce，也叫fold。
wikipedia链接：Fold (higher-order function)

SICP中用scheme实现的叫accumulate。
C++中是std::accumulate。

wiki中Folds in various languages部分讲了各种语言中的这个函数的叫法。 reduce在函数式语言里就是要减少的意思，要合并结果，多项变成一项。至于怎么合并，就看reduce的函数是什么。
range得到一个collection（或sequence），里面有多项。reduce函数是add，结果是一项。
当然reduce后也可以还是一个collection，那是因为把collection整体看做一项结果。 别纠结了，这个函数如此难懂，完全不符合python的风格，以致于在python3中被删除了。

题主还是趁早改邪归正，抛弃python2，投入python3的阵营吧！ reduce 在这里应该翻译成“归纳”。 verb (used with object), brought, bringing.
1.
to carry, convey, conduct, or cause (someone or something) to comewith, to, or toward the speaker:
Bring the suitcase to my house. He brought his brother to my office.
2.
to cause to come to or toward oneself; attract:
Her scream brought the police. He brought honor to his family by hisheroism.
3.
to cause to occur or exist:
The medication brought instant relief.
4.
to cause to come into a particular position, state, or effect:
to bring the car to a stop.
5.
to cause to appear or occur in the mind; evoke or recall:
The letter brought her memories of youth.
6.
to persuade, convince, compel, or induce:
She couldn't bring herself to sell the painting.
7.
to sell for; fetch:
These lamps will bring a good price.

Verb phrases
9.
bring about, to accomplish; cause:
Land reform brought about a great change in the lives of the commonpeople.
10.
bring around /round,

1. to convince of a belief or opinion; persuade:
   I think we can bring him around to agreeing with the plan.
   
2. to restore to consciousness, as after a faint.
3. to bring as a visitor:
   They brought around a new employee this morning.
   

11.
bring down,

1. to injure, capture, or kill:
   He brought down several ducks on his last hunting trip.
   
2. to lessen; reduce:
   I won't buy that lamp unless they bring down the price.
   
3. Slang. to cause to be in low spirits; depress:
   The bad news brought him down.
   

12.
bring forth,

1. to give birth to; deliver; bear:
   to bring forth a son.
   
2. to give rise to; introduce:
   to bring forth a proposal for reducing costs.
   

13.
bring forward,

1. to bring to view; show.
2. to present for consideration; adduce:
   to bring forward an opinion.
   

14.
bring in,

1. to yield, as profits or income:
   My part-time job doesn't bring in much, but I enjoy it.
   
2. to present officially; submit:
   The jury brought in its verdict.
   
3. to cause to operate or yield:
   They brought in a gusher on his property.
   
4. to present for consideration, approval, etc.; introduce:
   She brought in six new members last month.
   

15.
bring off, to accomplish, carry out, or achieve (something):
He brought off his speech with ease.
16.
bring on,

1. to cause to happen or exist; bring about:
   This incident will surely bring on a crisis.
   
2. to introduce; cause to appear:
   Bring on the clowns.
   

17.
bring out,

1. to expose; reveal.
2. to make noticeable or conspicuous in a contrast.
3. to publish, as a book or play.
4. to introduce officially into society:
   to bring out a debutante.
   

18.
bring to,

1. to bring back to consciousness; revive.
2. Nautical. to head (a vessel) close to or into the wind so as to halt.

19.
bring up,

1. to care for during childhood; rear.
2. to introduce or mention for attention, discussion, action, orconsideration.
3. to vomit.
4. to stop or cause to stop quickly:
   to bring up a car at the curb.
   
5. Nautical. (of a vessel) to cause to halt, as by lowering an anchor orrunning aground; fetch up.

....
reduce 很多项成一项啊。这个很难理解么？