在Python中，更有效的方法是：“键不在列表中”或“键不在列表中”？ [英] What's more efficient in Python: `key not in list` or `not key in list`?

问题描述

只是发现这两种语法方法都是有效的。

Just found out that both syntax ways are valid.

哪个效率更高？

element not in list

或：

not element in list

吗？

推荐答案

它们的行为相同，甚至产生相同的字节码；它们同样有效。也就是说，通常将不在列表中的元素。 PEP8对 not ... in 与 ... not 并没有具体的建议，但是不是...是而不是 ...不是和它更喜欢后者：

They behave identically, to the point of producing identical byte code; they're equally efficient. That said, element not in list is usually considered preferred. PEP8 doesn't have a specific recommendation on not ... in vs. ... not in, but it does for not ... is vs. ... is not, and it prefers the latter:

使用不是运算符，而不是 not ...是。虽然这两个表达式在功能上相同，但前者更具可读性和首选性。

Use is not operator rather than not ... is. While both expressions are functionally identical, the former is more readable and preferred.

要显示性能上的等效性，请执行快速字节码检查：

To show equivalence in performance, a quick byte code inspection:

>>> import dis
>>> dis.dis('not x in y')
  1           0 LOAD_NAME                0 (x)
              2 LOAD_NAME                1 (y)
              4 COMPARE_OP               7 (not in)
              6 RETURN_VALUE

>>> dis.dis('x not in y')
  1           0 LOAD_NAME                0 (x)
              2 LOAD_NAME                1 (y)
              4 COMPARE_OP               7 (not in)
              6 RETURN_VALUE

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