yield是什么

In computer science, yield is an action that occurs in a computer program during multithreading, of forcing a processor to relinquish control of the current running thread, and sending it to the end of the running queue, of the same scheduling priority.

引自维基百科：Yield (multithreading))，中文译文：

在计算机科学中，yield是发生在多线程程序中的一种情形：强制让处理器放弃对当前运行线程的控制，并把它发送到运行队列的尾部。（队列中的线程拥有相同的运行优先级）

关键字：放弃对线程的控制

generator是什么

In computer science, a generator is a special routine that can be used to control the iteration behaviour of a loop. In fact, all generators are iterators.[1] A generator is very similar to a function that returns an array, in that a generator has parameters, can be called, and generates a sequence of values. However, instead of building an array containing all the values and returning them all at once, a generator yields the values one at a time, which requires less memory and allows the caller to get started processing the first few values immediately. In short, a generator looks like a function but behaves like an iterator.

引自维基百科：Generator (computer programming))

出发点：为了节省内存。关键字：看起来像函数，行为像迭代器。

Python中的generator

Python中的generator需要借助于yield实现

  1. def countfrom(n):
  2.     while True:
  3.         yield n
  4.         n += 1

yield细节

基础用法

  1. def countfrom(n):
  2.     while True:
  3.         yield n  # 返回n，等待下一次取数，即”放弃线程控制权“
  4.         n += 1

接受输入

  1. def countfrom(n):
  2.     x = 'start'
  3.     while True:
  4.         x = yield x  # 第一次返回 start，后面接受输入到x，再返回x