用Python解释F1 2012 UDP数据包

Question

I am working on a project where in game telemetry data from F1 2012 is interpreted by Python and sent to an Arduino to display as a physical dashboard.

F1 2012 sends the data via UDP packets at address 127.0.0.1, port 20777.

I have a simple python program that reads the incoming packets:

import socket

UDP_IP = "127.0.0.1"
UDP_PORT = 20777

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

sock.bind((UDP_IP, UDP_PORT))

while True:
    data, addr = sock.recvfrom(1024)
    print ("Message:" data)

This outputs messages such as:

b'\xce\xb3T@\x00\x00\x00\x001K\xa7E\xa0\xf1\xf0\xbc\xa1\xc6\x13\xc4OY\x0b\xc3\xd5\xbf.D\xca\xe2\xc2;\xb0\x9109\xf0\x19\xbd\xbb\xdd8\xbb:q\x19M\xbf\x81t.933\x19\xbf\x1e,\x19\xbf\xc2\x82\x9d\xbc\x9c\x0fM?\xa2#H\xbc\xd6\x16x\xbe\x92hr\xba:\xa8\x88=X\xd7&?q$\xc7>\x82w#><\xe9\x1d>w\xc9\xb8\xa7Bh\x010\x00\x00\x00\x00kr\xb7\xaf\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80?\x00\x00\x80?\x96z\x98\xb9!f\x849\x00\x00\x00\x00\x8d\x8b5C'

I know this is a rather long output but it contains 38 parameters about the car which refresh 60 times a second. These are outlined in this website by someone working on a similar project.

I have looked for similar questions on stackeoverflow with outputs from UDP similar to mine and I was informed that the data had to be unpacked with a suitable format.

Reading this website , it seem that the data in the packets are all float types in C so I modified my original code in Python.

import socket
import struct

UDP_IP = "127.0.0.1"
UDP_PORT = 20777

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

sock.bind((UDP_IP, UDP_PORT))

while True:
    data, addr = sock.recvfrom(1024)
    output = struct.unpack('f', data)
    print ("Message:", output)

Unpack is given the format 'f' to assign the format of the incoming data based on information from this page: docs.python.org/3.2/library/struct.html#format-characters

This now produces the error:

struct.error: unpack requires a bytes object of length 4

I believe now that I am at a dead end and I do not know how to proceed.

Please help.

Answer 1

As the error message says: struct.error: unpack requires a bytes object of length 4 , you need to pass 4 bytes at a time.

Modify your code to send 4 bytes a time

while True:
    data, addr = sock.recvfrom(1024)
    # data is 1024 length bytearray, break into 4 bytes and get the output
    output = struct.unpack('f', data[0:4]) # 4 bytes at a time
    print ("Message:", output)