python - 为什么 yield 函数在 Python 中不需要括号？

Question

在 Python 中，我多次看到用于创建生成器的 yield 函数。这个函数和 print 函数在技术上都执行方法的操作，因为它们返回一个值。然而，在从 Python 2 到 Python 3 的转换过程中，print 函数像普通方法调用一样获得了括号，但 yield 保持不变。此外，yield 获得保留关键字的淡黄色，而 print 是保留方法的紫色。为什么 yield 不被视为一种方法并以这种方式着色而不使用括号语法？

(同理，为什么return也没有括号？)

让我再补充一些东西，yield 和 continue 在许多其他语言中也没有括号。我只是想知道是什么让它与众不同，而不是保留。还有许多其他的保留方法，它们有括号。

Answer 1

所以我开始寻找答案。 And it turns out, there is one .来自 PEP 255，给我们 yield 关键字的 pep

Q. Why a new keyword for "yield"? Why not a builtin function instead?

A. Control flow is much better expressed via keyword in Python, and yield is a control construct. It's also believed that efficient implementation in Jython requires that the compiler be able to determine potential suspension points at compile-time, and a new keyword makes that easy. The CPython referrence implementation also exploits it heavily, to detect which functions are generator- functions (although a new keyword in place of "def" would solve that for CPython -- but people asking the "why a new keyword?" question don't want any new keyword).

Q: Then why not some other special syntax without a new keyword? For example, one of these instead of "yield 3":

   return 3 and continue
   return and continue 3
   return generating 3
   continue return 3
   return >> , 3
   from generator return 3
   return >> 3
   return << 3
   >> 3
   << 3
   * 3

A: Did I miss one ? Out of hundreds of messages, I counted three suggesting such an alternative, and extracted the above from them. It would be nice not to need a new keyword, but nicer to make yield very clear -- I don't want to have to deduce that a yield is occurring from making sense of a previously senseless sequence of keywords or operators. Still, if this attracts enough interest, proponents should settle on a single consensus suggestion, and Guido will Pronounce on it.