In [129]: df
Out[129]:
CustNum CustomerName ItemQty Item Seatblocks ItemExt
0 32363 McCartney, Paul 3 F04 2:218:10:4,6 60
1 31316 Lennon, John 25 F01 1:13:36:1,12 1:13:37:1,13 300
In [130]: s = df['Seatblocks'].str.split(' ').apply(Series, 1).stack()
In [131]: s.index = s.index.droplevel(-1) # to line up with df's index
In [132]: s.name = 'Seatblocks' # needs a name to join
In [133]: s
Out[133]:
0 2:218:10:4,6
1 1:13:36:1,12
1 1:13:37:1,13
Name: Seatblocks, dtype: object
In [134]: del df['Seatblocks']
In [135]: df.join(s)
Out[136]:
CustNum CustomerName ItemQty Item ItemExt Seatblocks
0 32363 McCartney, Paul 3 F04 60 2:218:10:4,6
1 31316 Lennon, John 25 F01 300 1:13:36:1,12
1 31316 Lennon, John 25 F01 300 1:13:37:1,13