python实现串口通信 要导入serial的包 而且刚开始在等待接受收到0x45退出

import sys,threading,time;
import serial;
import binascii,encodings;
import re;
import socket;
from struct import *;

class ComThread:
def __init__(self, Port=1):
self.l_serial = None;
self.alive = False;
self.waitEnd = None;
self.port = Port;

def waiting(self):
if not self.waitEnd is None:
self.waitEnd.wait();

def SetStopEvent(self):
if not self.waitEnd is None:
self.waitEnd.set();
self.alive = False;
self.stop();

def start(self):
self.l_serial = serial.Serial();
self.l_serial.port = self.port;
self.l_serial.baudrate = 9600;
self.l_serial.timeout = 2;
self.l_serial.open();

if self.l_serial.isOpen():
self.waitEnd = threading.Event();
self.alive = True;
self.thread_read = None;
self.thread_read = threading.Thread(target=self.FirstReader);
self.thread_read.setDaemon(1);
self.thread_read.start();
return True;
else:
return False;

def FirstReader(self):
print "waiting data"
while self.alive:
time.sleep(0.01);
try:

data = '';
n = self.l_serial.inWaiting();
if n:
data = data + self.l_serial.read(n);
#for l in xrange(len(data)):
#    print '%02X' % ord(data[l]),
#snddata = '';
#snddata += chr(97)
#tt = 0x12345678;
#snddata += pack('i', tt)
#snddata += chr(0x64)
#print snddata;
#self.l_serial.write(snddata);
snddata= pack('i', 0x12345600)
snddata+= pack('B', 0x11)
self.l_serial.write(snddata);

if len(data) > 0 and ord(data[len(data)-1])==0x0a:
#pass;
break;

except Exception, ex:
print str(ex);

self.waitEnd.set();
self.alive = False;

def stop(self):
self.alive = False;
self.thread_read.join();
if self.l_serial.isOpen():
self.l_serial.close();

#
if __name__ == '__main__':
rt = ComThread();
try:
if rt.start():
rt.waiting();
rt.stop();
else:
pass;
except Exception,se:
print str(se);

if rt.alive:
rt.stop();

print '';
print 'End OK .';
del rt;