# 取前5個字符，跳過4個字符華，再取3個字符
format = '5s 4x 3s'

import struct
print struct.unpack(format, 'Test astring')
#('Test', 'ing')

import struct
theString = 'He is not very happy'
format = '2s 1x 2s 5x 4s 1x 5s'
print ' '.join(struct.unpack(format, theString))