Python Booleans

Question

在Python中，

if 1 and 2 not in {0, 1}:  # return True
print(True)
if 0 and 2 not in {0, 1}:  # return False
print(True)

不知道为什么有人能向我解释一下？

Answer 1

我想你的意思是：

if 1 not in {0, 1} and 2 not in {0, 1}:

按照您的方式，它正在解析(如果1(和(如果2不在｛0，1｝中("如果1〃；总是决心实现。

Answer 2

您可以使用all:

mySet = {0,1}
if not all(x in mySet for x in (1,2)):
print(True)
if not all(x in mySet for x in (0,2)):
print(True)

输出：

True
True

Answer 3

这是因为if由多个条件组成。1等于True，0等于False，它们大多可以互换使用。

因此：

1 and 2 not in {0, 1}
# is actually
(1) and (2 not in {0, 1})
# which equals to
(True) and (2 not in {0, 1})
# and both of them are True
True and True
# -------------------
# but in this case
0 and 2 not in {0, 1}
# is actually
(0) and (2 not in {0, 1})
# which equals to
(False) and (True)
# that is False

如果你想检查多个值是否在一个序列中，你应该这样做：

1 in {0, 1} and 2 in {0, 1}