列表索引超出范围

Question

How do I fix this error, pos_coordinates contains a list of values and the updatePos_coordinates is the previously pos_coordiantes values copied into the updatePos_coordinates list. I want to find the differences between the object and index value 8, 9, 12, and 13. but I kept on getting this error. How do I solve this

    screen_width = 0
    screen_height = 0
    updatePos_coordinates = []

    while True:
        client_socket.send("loc\n")
        data = client_socket.recv(8192)
        pos_coordinates = data.split()

        if(not(pos_coordinates[-1] == "eom" and pos_coordinates[0] == "start")):
            continue

        if (screen_width != int(pos_coordinates[2])):
            screen_width = int(pos_coordinates[2])
            screen_height = int(pos_coordinates[3])

        if (pos_coordinates != updatePos_coordinates):
            if(cmp(pos_coordinates[8:10], updatePos_coordinates[8:10]) == 0):
                both.brake()
                print "Ball is in the same location.."
            if((pos_coordinates[8] - updatePos_coordinates[8] > 5) or (pos_coordinates[8] - updatePos_coordinates[8] < -5) or (pos_coordinates[9] - updatePos_coordinates[9] > 5) or (pos_coordinates[9] - updatePos_coordinates[9] < -5)):     
                activateRobot(pos_coordinates)
            else:
                both.brake()
                print "Ball is in the same location.."

        updatePos_coordinates = pos_coordinates[:]
        time.sleep(3)
        print '...........'

and I keep on getting this:

Traceback (most recent call last):
  File "test.py", line 155, in <module>
    if((pos_coordinates[8] - updatePos_coordinates[8] > 5) or (pos_coordinates[8] - updatePos_coordinates[8] < -5) or (pos_coordinates[9] - updatePos_coordinates[9] > 5) or (pos_coordinates[9] - updatePos_coordinates[9] < -5)):     
IndexError: list index out of range

Answer 1

You are trying to access updatePos_coordinates[8] when it doesn't have any elements yet, as it hasn't been changed since you defined it as updatePos_coordinates = [] .

You should fill updatePos_coordinates with default values before the loop.

For example:

updatePos_coordinates = ['' for _ in range(16)]
# replace 16 with length of pos_coordinates

Alternatively, you could just make both coordinates equal to each other the first time through the loop.

if len(updatePos_coordinates) < 16:
    updatePos_coordinates = pos_coordinates[:]

elif pos_coordinates != updatePos_coordinates:
    ...

I've also noticed that you are treating the coordinates like integers, when they are actually strings.