SerialData.py

from threading import Thread
import serial
import sys
import time

DEBUG = False

buf = ''
def rx(ser):
	"""Receive serial data"""
	global buf
	tmpbuf = ''
	while ser:
		time.sleep(0.001)
		# Keep reading until an entire line is in the buffer, then return the last line
		tmpbuf = tmpbuf + ser.read(size=ser.inWaiting())
		if '\n' in tmpbuf:
			lines = tmpbuf.split('\n')
			buf = lines[-2]
			tmpbuf = lines[-1]
			if DEBUG:
				print "Serial data:\n%s" % lines[-2]

class SerialData(object):
	"""Handle the serial port"""
	def __init__(self, port, baudrate, bytesize, parity, stopbits, xonxoff, rtscts, debug):
		global DEBUG
		self.port = port
		self.baudrate = baudrate
		self.bytesize = bytesize
		self.parity = parity
		self.stopbits = stopbits
		self.xonxoff = xonxoff
		self.rtscts = rtscts
		self.ser = None
		self.buf = ''
		self.debug = debug
		DEBUG = self.debug
		
		try:
			self.ser = ser = serial.Serial(
				port = self.port,
				baudrate = self.baudrate,
				bytesize = self.bytesize,
				parity = self.parity,
				stopbits = self.stopbits,
				timeout = 0.1,
				xonxoff = self.xonxoff,
				rtscts = self.rtscts,
				interCharTimeout = None
			)
		except serial.serialutil.SerialException:
			# no serial connection
			self.ser = None
		else:
			Thread(target=rx, args=(self.ser,)).start()
			
	def next(self):
		if not self.ser:
			print "Serial port connection failure"
			sys.exit(-1)
		try:
			return float(buf.split(',')[0].strip())
		except ValueError:
			print 'Invalid data: ', buf
	
	def __del__(self):
		if self.ser:
			self.ser.close()