>>> D = {'a':1, 'b':2, 'c':3}
>>> D['a']
1
>>> D['d']
Traceback (innermost last):
  File "<stdin>", line 1, in ?
KeyError: d
>>> D['d'] = 4
>>> D
{'b': 2, 'd': 4, 'a': 1, 'c': 3}
>>>
>>> L = [0,1]
>>> L[2]
Traceback (innermost last):
  File "<stdin>", line 1, in ?
IndexError: list index out of range
>>> L[2] = 3
Traceback (innermost last):
  File "<stdin>", line 1, in ?
IndexError: list assignment index out of range