Python`if x is not None`或`if not is is None`？[关闭]

Python`if x is not None`或`if not is is None`？[关闭]

性能没有差异，因为它们可以编译为相同的字节码：

>>> import dis>>> dis.dis("not x is None")  10 LOAD_NAME     0 (x)   2 LOAD_ConST    0 (None)   4 COMPARE_OP    9 (is not)   6 RETURN_VALUE>>> dis.dis("x is not None")  10 LOAD_NAME     0 (x)   2 LOAD_ConST    0 (None)   4 COMPARE_OP    9 (is not)   6 RETURN_VALUE

从风格上讲，我尝试避免

not x is y

，人类读者可能会误以为

(not x) is y

。如果我写的

x is not y

话就没有歧义。