如下的yield生成器会出错?

Question

PEP342将yield升级成了一个表达式

def test():
    print((yield))

---

为什么下面的yield不加括号会出错

def test():
    print(yield)

Answer 1

yield 必须用加括号变成 yield_atom 才能用作子表达式。

---

expression

atom      ::=  identifier | literal | enclosure
enclosure ::=  parenth_form | list_display | dict_display | set_display
               | generator_expression | yield_atom
yield_atom       ::=  "(" yield_expression ")"
yield_expression ::=  "yield" [expression_list | "from" expression]