>>> import subprocess, signal
>>> signal.signal(signal.SIGCLD, signal.SIG_IGN)
0
>>> subprocess.Popen(['echo','foo']).wait()
foo
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "./Lib/subprocess.py", line 1229, in wait
    pid, sts = _eintr_retry_call(os.waitpid, self.pid, 0)
  File "./Lib/subprocess.py", line 482, in _eintr_retry_call
    return func(*args)
OSError: [Errno 10] No child processes


You're right, I fixed something giving the same ECHILD error in multiprocessing. But it was not related.