Initialize serial device
import serial
#Serial takes two parameters: serial device and baudrate
ser = serial.Serial('/dev/ttyUSB0', 9600)
to read single byte from serial device
data = ser.read()
to read given number of bytes from the serial device
data = ser.read(size=5)
to read one line from serial device.
data = ser.readline()
to read the data from serial device while something is being written over it.
#for python2.7
data = ser.read(ser.inWaiting())
#for python3
ser.read(ser.inWaiting)