SIGCHLD is a more portable name than SIGCLD (OSX has no SIGCLD).

Lib/test/subprocessdata/sigchild_ignore.py

@@ -2,5 +2,5 @@ import signal, subprocess, sys
 # On Linux this causes os.waitpid to fail with OSError as the OS has already
 # reaped our child process.  The wait() passing the OSError on to the caller
 # and causing us to exit with an error is what we are testing against.
-signal.signal(signal.SIGCLD, signal.SIG_IGN)
+signal.signal(signal.SIGCHLD, signal.SIG_IGN)
 subprocess.Popen([sys.executable, '-c', 'print("albatross")']).wait()