[Python] 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_ports
while 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.

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