python base

Truthy and falsy values

The following values are evaluated to False in Python:

constants defined to be false: None and False,
zero of any numeric type: 0, 0.0,
empty sequences and containers: "", [], {}.

or & and 的用法

truthy_integer = False or 5 and 100  # 100

结果为什么是100呢？and有限级比or高，所以执行的顺序是 5 and 100 ,返回的是 100，然后是False or 100,所以结果是 100

懒惰执行规则

# division is never evaluated, because the first argument is True
lazy_or = True or (1 / 0)  # True
 
# division is never evaluated, because the first argument is False
lazy_and = False and (1 / 0)  # False

总结一下大概是 and时，返回第一个非True,如果都是True,返回最后遇到的True值 Flase and 1 = False, True and 2 = 2, 2 and False = False, 2 and 3 = 3 or时，返回第一个非Flase，如果都是Flase，返回最后一个Flase值 False or None = None ，都是false，返回最后一个False值，也就是None

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