>>> word = "Python"

>>> word[:2]  # character from the beginning to position 2 (excluded)

'Py'

>>> word[4:]  # characters from position 4 (included) to the end

'on'

>>> word[-2:] # characters from the second-last (included) to the end

'on'

>>> word[:2]  # 从开始到2位置

'Py'

>>> word[4:]  # 从4到末尾

'on'

>>> word[-2:] # 从-2到末尾

'on'

 | P | y |  t |  h | o | n |

 0   1   2   3   4   5    6

-6  -5  -4  -3  -2  -1