Terminating a program within python

Hi I embeded a time constraint in to my python code which is running a fortran code with a function. However I realized that the function that puts a time constraint on the other function doesn't terminates the code, just leaves it in background and skips it instead. What I want to do is terminate the code, when it exceed the constrained time. Here is the code that I'm using to constrain time which is taken from here.

def timeout(func, args=(), kwargs={}, timeout_duration=15, default=1):
    import signal

    class TimeoutError(Exception):
        pass

    def handler(signum, frame):
        raise TimeoutError()

    # set the timeout handler                                                                                                                                             
    signal.signal(signal.SIGALRM, handler)
    signal.alarm(timeout_duration)
    try:
        result = func(*args, **kwargs)
    except TimeoutError as exc:
        result = default
    finally:
        signal.alarm(0)

    return result

I looked up popen.terminate(), sys.exit() and atexit.register() but couldn't figure out how it will work with this piece of code which I tried to add in part below that I showed in comment.

...
        result = func(*args, **kwargs)
    except TimeoutError as exc:
        result = default
#add the terminator
    finally:
...

NOTE: Function is inside a for loop chain so I dont want to kill whole python session but just want to kill the program that this function runs which is a fortran code and skip to the other element in the for loop chain.

Part below added after some comments and answers:

I tried to add SIGTERM with popen.terminate() however it terminated all python session which I just want to terminate current running session and skip to the other elements in the for loop. what I did is as follows:

...
    signal.signal(signal.SIGTERM, handler) 
    signal.alarm(timeout_duration)
    try:
        result = func(*args, **kwargs)
    except TimeoutError as exc:
        result = default
        popen.terminate()
...