假设我有一根绳子：>>>a = 'akwkwas'

>>>

>>>a[-3:]

'was'

>>>a[-3:None]

'was'

>>>a[-3:0]

''

为什么我不能用0作为切片的结尾？

这是来自文档：One way to remember how slices work is to think of the indices as pointing between characters, with the left edge of the first character numbered 0. Then the right edge of the last character of a string of n characters has index n, for example:+---+---+---+---+---+---+

| P | y | t | h | o | n |

+---+---+---+---+---+---+

0 1 2 3 4 5 6

-6 -5 -4 -3 -2 -1The first row of numbers gives the position of the indices 0...6 in the string; the second row gives the corresponding negative indices. The slice from i to j consists of all characters between the edges labeled i and j, respectively.

因此，当我们在循环中使用负索引时，我们应该检查结束值，因为负索引中的结束0不存在，例如当我们将字符串拆分为类似金钱的字符串时：>>>a = '12349878334'

>>>print(','.join([a[-i-3:-i if i else None] for i in range(0, len(a), 3)][::-1]))

>>>12,349,878,334