人们使用是是因为使用 == 没有优势。可以编写比较等于 None 的对象，但不常见。

The reason people use is is because there is no advantage to using ==. It is possible to write objects that compare equal to None, but it is uncommon.

class A(object):
    def __eq__(self, other):
        return True

print A() == None

输出：

True

是不要认为这个事实很重要。

The is operator is also faster, but I don't consider this fact important.