python - 对于每个原始类型，Python 将什么视为 True 或 False？

Question

def toBeOrNotToBe(x, y):
    return x or y

print(toBeOrNotToBe(0,1))
print(toBeOrNotToBe([],[1,2,3]))
print(toBeOrNotToBe('','something'))
print(toBeOrNotToBe(None, lambda _: None))

1
[1, 2, 3]
something
<function <lambda> at 0x0000015A20538708>

在哪里可以找到 Python 认为每种类型的 True 或 False 的完整列表？ 如何为我的类编写自己的方法？

Answer 1

Truth Value Testing

Any object can be tested for truth value, for use in an if or while condition or as operand of the Boolean operations below.

By default, an object is considered true unless its class defines either a __bool__() method that returns False or a __len__() method that returns zero, when called with the object. Here are most of the built-in objects considered false:

• constants defined to be false: None and False.

• zero of any numeric type: 0, 0.0, 0j, Decimal(0), Fraction(0, 1)

• empty sequences and collections: '', (), [], {}, set(), range(0)

Operations and built-in functions that have a Boolean result always return 0 or False for false and 1 or True for true, unless otherwise stated. (Important exception: the Boolean operations or and and always return one of their operands.)

More details can be found here