issue when use your library

[newbie15]

iam try to use your S71200.py file and do simple data request like this

import S71200
from time import sleep
import snap7
from snap7.util import *
import struct

plc = S71200.S71200("192.168.0.180")
print plc.getMem('MW50')

Traceback (most recent call last):
File "program.py", line 15, in
print plc.getMem('MW50') # read memory bit M0.1
File "E:\My Job\CAN\python-program\S71200.py", line 65, in getMem
return get_int(mbyte,start)
File "C:\Python27\lib\site-packages\snap7\util.py", line 148, in get_int
value = struct.unpack('>h', struct.pack('2B', *data))[0]
struct.error: pack expected 2 items for packing (got 0)

but ended like that. is anything wrong with my configuration?