Serial con python para conectar con Arduino de forma sencilla y simple

Código más simple para conectar:
import serial
arduino = serial.Serial('com3', baudrate=57600, timeout=1.0)
while True:
    line = arduino.readline()
    print(line)



Código para enviar y recibir datos desde Arduino a Python por el serial:

import serial
import msvcrt # to detect keys pressed
import time # to execute time functions ( gives the ability to use delay-like commands )

print("Connecting to Arduino....") # print(something
arduino = serial.Serial('com3', baudrate=57600, timeout=1.0)
time.sleep(2)# wait for 2 seconds
print("Connected Successfully!")

while True:
    line = arduino.readline()
    print(line)
    if msvcrt.kbhit(): # if a key is pressed
        keypress = ord(msvcrt.getch()) # store the ASCII value of the character into our variable keypress
        if keypress == 119: #if 'w' is pressed (ASCII value of 'w' is 119)
            print('up') #simply print('up' in command prompt
            arduino.write('w'.encode('ascii')) #send 'w' to Arduino
        if keypress == 115: #if 's' is pressed (ASCII value of 's' is 115)
            print('down') #simply print('down' in command prompt
            arduino.write('s'.encode('ascii')) #send 's' to Arduino
        if keypress == 97: #if 'a' is pressed (ASCII value of 'a' is 97)
            print('left') #simply print('left' in command prompt
            arduino.write('a'.encode('ascii')) #send 'a' to Arduino
        if keypress == 100: #if 'd' is pressed (ASCII value of 'd' is 100)
            print('right') #simply print('right' in command prompt
            arduino.write('d'.encode('ascii'))  #send 'd' to Arduino
        if keypress == 101: #if 'e' is pressed (ASCII value of 'e' is 101)
            print('stop') #simply print('stop' in command prompt
            arduino.write('e'.encode('ascii')) #send 'e' to Arduino


Ojo con la decodificación a ascii con bytes para enviar al Arduino:

date_string = str(datetime.datetime.now())
dates_bytes = date_string.encode('ascii')
ser.write(date_bytes)

http://stackoverflow.com/questions/34653568/error-writing-to-serial-device-in-python 

Captura de Teclas Teclado desde python:
http://www.robotshop.com/letsmakerobots/a-guide-to-building-python-apps-for-controlling-your-robot


Referencia que puede servir:
http://pybonacci.org/2014/01/19/leer-datos-de-arduino-desde-python/