小编sai*_*ttu的帖子

a='0123456789'

>>> a
'0123456789' 

>>> a[1:-6:1] # working as expected
'123'

>>> a[2:-1:-1] # i was expecting '210' as answer based on start index=2 end index=0
''

请帮助理解第二个切片操作符如何返回任何内容