>>> a=[]
>>> a.append(9)
>>> a.append(21)
>>> a.append(7)
>>> a.append(2)
>>> a.append(5)
>>> a.append(7)
>>> a.append(11)
>>> a.append(7)
>>> a.append(9)
>>> print a
[9, 21, 7, 2, 5, 7, 11, 7, 9]
>>> a.sort()
>>> print a
[2, 5, 7, 7, 7, 9, 9, 11, 21]
>>> a_sin_repetir=[]
>>> for elemento in a:
...     if elemento not in a_sin_repetir:
...             a_sin_repetir.append(elemento)
...
>>> print a
[2, 5, 7, 7, 7, 9, 9, 11, 21]
>>> print a_sin_repetir
[2, 5, 7, 9, 11, 21]
>>>