Try look at the youtuber sciguy14 and one of his most recent videos is of the competition he entered where he interfaced arduino with python to get data off Facebook. There is example code from both.
There are two videos that have the source code, both has the name Facebook hackathon.
In python just have to do this:
1 - Import library:
import serial
2 - Open port:
ser = serial.Serial('/dev/ttyUSB0', 38400, timeout=1)
Setting the correct port and baudrate.
3 - Read data:
read = ser.read(X)
Where X is the number of bytes you want to read together. If you just write read = ser.read(), you read 1 byte.
I recommend you to read just one byte at a time because if you read more than one, it will kept as string and you cannot modify it. For avoiding it and be able to modify you have to save it as list but I haven't the code here right now.
And, the rest is treat that data in functions or whatever you want.
Some serial test program I found someday on the net, I do not recall where ... Should get you started
import time
import serial, sys, os
# configure the serial connections (the parameters differs on the device you are connecting to)
ser = serial.Serial(4, baudrate=9600, timeout=100)
ser
#ser.open()
ser.isOpen()
print 'Enter your commands below.\r\nInsert "exit" to leave the application.'
input=1
while 1 :
# get keyboard input
input = raw_input(">> ")
    # Python 3 users
    # input = input(">> ")
if input == 'exit':
ser.close()
exit()
else:
# send the character to the device
# (note that I happend a \r\n carriage return and line feed to the characters - this is requested by my device)
ser.write(input + '\r\n')
out = ''
# let's wait one second before reading output (let's give device time to answer)
time.sleep(1)
while ser.inWaiting() > 0:
out += ser.read(1)
if out != '':
print ">>" + out