Python中的扩展切片语法

Question

我在处理一些弦，弄不懂切片是怎么工作的， 以下输出“i”

“输入”[0:：-1]

鉴于以下输出“tupni”

“输入”[：：-1]

我不知道的是第一个，以及负指数的切片是如何工作的

Answer 1

也许这些例子可以说明这一点：

In [146]: "input"[::-1] # from back to the begining. Equivalent to: "input"[len("input")::-1]
Out[146]: 'tupni'

In [147]: "input"[0::-1] # from back to the 0'th (i.e. first) element from back
Out[147]: 'i'

In [148]: "input"[1::-1] # from back to the 2ed element from back
Out[148]: 'ni'

In [151]: "input"[len("input")::-1] # from back to the last element from back (alterantive way)
Out[151]: 'tupni'