帮忙看一下这个简单的例子

yudianzhiyu

word = 'Help' + 'A'

word[2:1]的输出为什么会是空呢

pywugw

s[i:j]         slice of s from i to j

If i or j is negative, the index is relative to the end of the string: len(s) + i or len(s) + j is substituted. But note that -0 is still 0.

The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s). If i is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty.