how to map the character a->b, b->c,.....z->a in python string code example

Example 1: all characters python

'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

Example 2: python char at

>>> s = "python"
>>> s[3]
'h'
>>> s[6]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: string index out of range
>>> s[0]
'p'
>>> s[-1]
'n'
>>> s[-6]
'p'
>>> s[-7]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: string index out of range
>>>