>>> Fib()[5]
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: 'Fib' object does not support indexing

class Fib(object):
  def __getitem__(self, n):
    a, b = 1, 1
    for x in range(n):
      a, b = b, a + b
    return a

>>> f = Fib()
>>> f[0]
1
>>> f[1]
1
>>> f[2]
2
>>> f[3]
3
>>> f[10]
89
>>> f[100]
573147844013817084101

class _List(object):

  def __getitem__(self, key):
    print key

l = _List()
l[3]  # print 3

l[1:4] # print slice(1, 4, None)

a = slice(1, 4, None)

range(5)[a] # print [1, 2, 3]

class _List(object):
  
  def __init__(self, _list):
    self._list = _list

  def __getitem__(self, key):
    if isinstance(key, int):
      return self._list[key]
    elif isinstance(key, slice):
      reutrn self.__class__(self._list[key])

if __name__ == '__main__':
  c = _List(range(10))
  b = c[1:5]
  print b[3] # print 4