python读写串口

#!/usr/bin/python
import serial
from time import sleep

ser = serial.Serial('/dev/ttyUSB0', 9600, timeout=0.5) 

print ser.port
print ser.baudrate

def recv(serial):  
  while True:  
    data =serial.read(42)  
    if data == '':  
      continue
    else:
      break
    sleep(0.02) 
  return data 

while True:  
  data =recv(ser) 
  if data != '': 
    print data
    ser.write(data)