Cannot open pipe descriptors created by threads in Python

Cannot open pipe descriptors created by threads in Python

I just began to study the pipe method of python. I tried to wrap the pipe
descriptors into file object and read by line.
import os,time,threading
def child():
while True:
time.sleep(1)
msg = ('Spam\n' ).encode()
os.write(pipeout,msg)
def parent():
while True:
a = os.fdopen(pipein)
line = a.readline()[:-1]
print('Parent %d got [%s] at %s' % (os.getpid(),line,time.time()))
pipein,pipeout = os.pipe()
threading.Thread(target=child,args=()).start()
parent()
when I run the script, the results are following----the script just works
in the first iteration then shows the error messages
Parent 621 got [Spam] at 1376785841.4
Traceback (most recent call last):
File "/Users/miteji/pipe-thread.py", line 43, in <module>
parent()
File "/Users/miteji/pipe-thread.py", line 36, in parent
line = a.readline()[:-1]
IOError: [Errno 9] Bad file descriptor
>>> Exception in thread Thread-1:
Traceback (most recent call last):
File
"/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py",
line 551, in __bootstrap_inner
self.run()
File
"/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py",
line 504, in run
self.__target(*self.__args, **self.__kwargs)
File "/Users/miteji/pipe-thread.py", line 30, in child
os.write(pipeout,msg)
OSError: [Errno 32] Broken pipe
So where is the problem? why the pipe is broken? Thank you all!