Python: attempting to open serial caused IOError: [Errno 6] Device not configured

I trying to open two serial ports in Python with the following code:

for i in range(0, 2):    if platform.system() == "Darwin":        pos = 2+i    else:        pos = i    port = serial.Serial(current_ports[pos], BAUD_RATE, timeout=TIMEOUT)    time.sleep(1.516)    port.write('#')    time.sleep(1.516)    out = ''    print "Reading MAC Address...."    while port.inWaiting() > 0:        out += port.read(1)        print out    if out == '04:E9:E5:00:EC:51':        led_port = port    elif out == '04:E9:E5:01:0C:E0':        matrix_port = port   

Sometimes the ports open successfully, sometimes they don't. When they don't, I get this error message:

Reading MAC Address....Traceback (most recent call last):  File "animation.py", line 227, in <module>    main()  File "animation.py", line 208, in main    led_port, matrix_port = get_ports()  File"/Users/collinschupman/Documents/FutureCities/MurmurWall/Onsite/Raspi/helper_functions.py", line 41, in get_portswhile port.inWaiting() > 0: File "/Library/Python/2.7/site-packages/serial/serialposix.py", line 449, in inWaiting    s = fcntl.ioctl(self.fd, TIOCINQ, TIOCM_zero_str)IOError: [Errno 6] Device not configured

As you can see, it gets to the inWaiting() call and then throws this error.

For a little reference, the code is sending a message to a couple Arduinos so they can be identified by their MAC addresses.

Is there anything blatantly incorrect I'm doing Python-side which would cause this setup to fail once and a while? I'd say this code works 50% of the time right now.

Thanks,

Collin