multiple delimiters pandas

1>>> !cat castle.dat
2c stuff
3c more header
4c begin data         
5 1 1:.5
6 1 2:6.5
7 1 3:5.3
8>>> df = pd.read_csv('castle.dat', skiprows=3, names=['a', 'b', 'c'], 
9                     sep=' |:', engine='python')
10>>> df
11   a  b    c
120  1  1  0.5
131  1  2  6.5
142  1  3  5.3
15