>>> s = 'abcdefgh'
>>> n, m, char, chars = 2, 3, 'd', 'cd'
>>> # starting from n=2 characters in and m=3 in length;
>>> s[n-1:n+m-1]
'bcd'
>>> # starting from n characters in, up to the end of the string;
>>> s[n-1:]
'bcdefgh'
>>> # whole string minus last character;
>>> s[:-1]
'abcdefg'
>>> # starting from a known character char="d" within the string and of m length;
>>> indx = s.index(char)
>>> s[indx:indx+m]
'def'
>>> # starting from a known substring chars="cd" within the string and of m length.
>>> indx = s.index(chars)
>>> s[indx:indx+m]
'cde'
>>>
