[Tutor] how to transform the data as below?

[Peter Otten]

Yeh wrote:

> Hi,
> 
> I got messages from a MCU by using codes below:
> 
> import socket
> import time
> 
> port = 8888
> s = socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
> s.bind(("",port))
> print('waiting on port:', port)
> while True:
> data, addr = s.recvfrom(1024)
> print("DATA:", data, addr)
> time.sleep(100)
> 
> The messages should be a head "YY" and 5 integers, (each integer is
> transferred by 2 bytes.) but I got data below. So, how to transform the
> data? and how to arrange the data to a array?
> 
> DATA:
> b'\t\x01x\x01\xfd\x02\x01\x02[YY\x01\t\x01x\x01...
> ('192.168.1.101', 35000)


What you read are the raw bytes. The array module offers one way to convert 
bytes to integers. Unfortunately the separator byte sequence b"YY" (or b"XY" 
followed by b"YZ") is also that for the integer 22873:

>>> array.array("H", b"YY")
array('H', [22873])

Therefore you cannot be 100% sure when you start the bytes-to-int conversion 
at the first occurence of b"YY". Here's an example that uses a simple 
heuristics (which may fail!) to cope with the problem


import array, re

def find_start(data):
    for m in re.compile(b"YY").finditer(data):
        if all(
                data[i:i+2] == b"YY"
                for i in range(m.start(), len(data), 12)):
            
            return m.start()
    raise ValueError



data = b'\t\x01x\x01\xfd\x02\x01\x02[YY\x01\t...

if __name__ == "__main__":
    start = find_start(data)
    for i in range(start, len(data)-11, 12):
        chunk = data[i:i+12]
        print(chunk, "-->", list(array.array("H", chunk[2:])))