代码中经常会有变量是否为None的判断,有三种主要的写法:
第一种是`if x is None`;
第二种是 `if not x:`;
第三种是`if not x is None`(这句这样理解更清晰`if not (x is None)`) 。
如果你觉得这样写没啥区别,那么你可就要小心了,这里面有一个坑。先来看一下代码:
>>> x = 1
>>> not x
False
>>> x = [1]
>>> not x
False
>>> x = 0
>>> not x
True
>>> x = [0] # You don't want to fall in this one