Python core dump on sys.exit() from signal handler

I am seeing python core dump for a seemingly harmless program. I have written following piece of code to demonstrate my problem:

proc = None

def __signalHandler(signum, frame):
   print "In __signalHandler"

   if proc is not None:
      print "Send signal to BG proc"
      os.killpg(os.getpgid(proc.pid), signal.SIGINT)

      print "Wait for it to finish"
      proc.communicate()

   print "sys exit"
   sys.exit(130)

signal.signal(signal.SIGINT, __signalHandler)

# Start the process
proc = subprocess.Popen(["a.out"],
                        stdout=subprocess.PIPE,
                        stderr=subprocess.PIPE,
                        preexec_fn=os.setsid)

while proc.poll() is None:
   try:
      print proc.stdout.readline()
   except:
      print "Exception caught"

print "Done!"

a.out is a executable that prints statement and sleeps in a loop:

int main(int argc, char* argv[])
{
   for (int i = 0; i < 100; i++)
   {
      printf("Sleeping...\n");
      std::cout.flush();
      usleep(500000);
   }

   return 0;
}

Following is the output I get when I run the python code (I run the python program and then press Ctrl-C so that the signal handler gets invoked):

$ python sample.py
Sleeping...
Sleeping...
Sleeping...
^CIn __signalHandler
Send signal to BG proc
Wait for it to finish
sys exit
Segmentation fault (core dumped)

Does anyone have a clue why python core dumps? Is there any way to fix this? My guess is that the exception thrown from sys.exit() is somehow causing a problem. os._exit() doesnt have the same issue. However, I am trying to find out the exact reason behind this behaviour.

For what it's worth, I am using Python 2.7.3

This version works: interrupting the top-level program correctly prints "sys exit", and output of the subprocess is printed line by line.

source

import os, signal, subprocess, sys

proc = None

def __signalHandler(signum, frame):
   print "In __signalHandler"

   if proc is not None:
      print "Send signal to BG proc"
      os.killpg(os.getpgid(proc.pid), signal.SIGINT)

      print "Wait for it to finish"
      proc.communicate()

   print "sys exit"
   sys.exit(130)

signal.signal(signal.SIGINT, __signalHandler)

# Start the process
proc = subprocess.Popen('ping -c3 8.8.8.8'.split(),
                        stdout=subprocess.PIPE,
                        stderr=subprocess.PIPE,
                        preexec_fn=os.setsid)

while proc.poll() is None:
   try:
      print proc.stdout.readline(),
   except Exception as exc:
      print 'Exception caught: {}'.format(exc)

print "Done!"

output

$ python ./sub5.py 

PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=43 time=48.0 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=43 time=48.3 ms
^CIn __signalHandler
Send signal to BG proc
Wait for it to finish
sys exit

$ echo $?
130