Python lists don't implement extended slices, try numpy arrays:

>>> import numpy as np
>>> x = array([[1,2,3], [4,5,6]])
>>> x[:, 2]
array([3, 6])
>>> 
>>> lst = [[1,2,3], [4,5,6]]
>>> lst[:, 2]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list indices must be integers or slices, not tuple
>>> 

Was there any issue apart from the extended slices?