import os, subprocess, signal

def setSigPipe():
    "enable sigpipe exit in current process"
    signal.signal(signal.SIGPIPE, signal.SIG_DFL)
    if signal.getsignal(signal.SIGPIPE) != signal.SIG_DFL:
        raise Exception("SIGPIPE could not be set to SIG_DLF")


# p1 should write until SIGPIPE is received
p1 = subprocess.Popen(["yes"], stdout=subprocess.PIPE, preexec_fn=setSigPipe, close_fds=True)
# p2 exits immediatly with and error
p2 = subprocess.Popen(["false"], stdin=p1.stdout, close_fds=True)

# this hangs because p1.stdout is still open in parent process, preventing
# SIGPIPE from being generated.
w1 = p1.wait()
print "wait1",w1
w2 = p2.wait()
print "wait2",w2