os.fork on linux defunct

[Ray]

I'm running python 2.4 on linux. I use python os.fork run tcpdump, but
after I kill the forked process (tcpdump) in linux it shows defunct

here is the code:

#!/usr/bin/python
import time, os
class Test:
    def fork(self):
        self.pid=os.fork()
        if self.pid=0:
            args=['tcpdump', '-i', 'eth0', 'port', '80' '']
            os.execl("/usr/sbin/tcpdump", *args)
            os._exit(0)
    def kill(self):
        os.kill(self.pid, 15)
if __name__=='__main__':
    while True:
        test=Test()
        test.fork()
        time.sleep(2)
        test.kill()
        time.sleep(30)

after I call kill() it will kill tcpdump (capture will stop) but on
linux, ps shows tcpdump as defunct process
what am I missing?

thanks for any help.