docs: def forkexec(argv, env=None):
      """Fork a child process."""
      child_pid = os.fork()
      if child_pid == 0:
          os.closerange(3, MAXFD)
          environ = os.environ.copy()
          if env is not None:
              environ.update(env)
          os.execve(argv[0], argv, environ)
      return child_pid