Purely integer-location based indexing for selection by position. .iloc[] is primarily integer position based (from 0 to length-1 of the axis), but may also be used with a boolean array.
>>> df.iloc[[0, 1]] a b c d 0 1 2 3 4 1 100 200 300 400
>>> df.iloc[1:3, 0:3] a b c 1 100 200 300 2 1000 2000 3000
