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改为python 3的过程中，print函数像普通方法调用一样获得了括号，但yield保持不变。另外，yield获得保留关键字的黄色，而print是保留方法的紫色。为什么yield不被认为是一种方法，并用这种方式着色，而不使用括号语法？

(同样的情况下，为什么return也缺少括号？)

让我再添加一些东西，yield和continue在许多其他语言中也没有括号。我只想知道是什么让它与众不同，除了它是保留的。有许多其他的保留方法可以得到括号。

所以我开始寻找答案。结果是，有一个。从PEP 255，给我们提供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":

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.

print不是带括号的函数：它从一个语句变成了一个函数。yield仍然是一个声明，就像return一样。语法突出显示是特定于开发环境的。

您可以在这里找到关于表达式和语句之间差异的更多信息，以及关于函数和语句之间差异的更多信息。另请参见有关简单语句和复合语句的文档。

yield不是函数，它是关键字，根据语法，它不需要括号。-

yield_atom ::= "(" yield_expression")"

yield_expression ::="yield" [expression_list]

print曾是python 2中的一条语句，但后来改为python 3中使用pep 3105的内置函数。

print是python 2语言规范定义的关键字，并成为python 3的内置函数(由标准库规范定义)。yield过去是，现在仍然是一个关键字。