>>> xs = 'abcde'

>>> xs[0]
'a'
>>> xs[-1]
'e'
>>> xs[4]
'e'
>>> xs[5]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: string index out of range
>>> xs[-6]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: string index out of range

>>> xs[3:]
'de'
>>> xs[4:]
'e'
>>> xs[5:]
''