>>>import struct
>>>size_a = struct.calcsize('10s')
size_a = 10
>>>size_b = struct.calcsize('iii')
size_b = 12
>>>size_c = struct.calcsize('10siii')
size_c = 24

Offset: 0 1 2 3 4 5 6 7 8 9
        s----------------->

1 1 1 1 1 1 1 1 1 1 2 2 2 2
Offset: 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
        s-----------------> x x i-----> i-----> i----->