human
I wrote the below code

    if (POSIX and use_sigalrm):
        def sigalrm_handler(signum, frame):
            raise TimeoutError()
        def deco(func):
            def wrap(*a, **kw):
                old_handler = signal.signal(signal.SIGALRM, sigalrm_handler)
                signal.setitimer(signal.ITIMER_REAL, timeout)
                try:
                    return func(*a, **kw)
                except TimeoutError:
                    return return_val
                finally:
                    signal.setitimer(signal.ITIMER_REAL, 0)
                    signal.signal(signal.SIGALRM, old_handler)
            return wrap
    else:
        def deco(func):
            def wrap(*a, **kw):
                start_time = time.time()
                def trace(frame, event, arg):
                    if ((time.time() - start_time) > timeout):
                        raise TimeoutError()
                    return trace
                sys.settrace(trace)
                try:
                    return func(*a, **kw)
                except TimeoutError:
                    sys.settrace(None)
                    return return_val
                finally:
                    sys.settrace(None)
            return wrap
    return deco

What's a good function header?
assistant
#Here's a good function header.

def time_limited(timeout=0.5, return_val=np.nan, use_sigalrm=True):