crcmodbus.py

#!/usr/bin/python3
# Note: This code should also work with python 2

def crc16modbus(data, poly=0xA001, crc=0xFFFF):
    data = bytearray(data)

    for b in data:
        crc ^= (0xFF & b)
        for _ in range(0, 8):
            if (crc & 0x0001):
                crc = ((crc >> 1)  & 0xFFFF) ^ poly
            else:
                crc = ((crc >> 1)  & 0xFFFF)

    return crc & 0xffff

instr=b'\x30\x31\x32\x33\x34\x35\x36\x37\x38\x39'
print ("CRC: 0x%04x" % crc16modbus(instr))