def timer(string,i,f):
    """
    Takes in:
        i = starting time;
        f = finishing time.
    Returns: Time taken in full minutes and seconds.
    """
    sec = f - i     # Total time to run.
    mins, sec= divmod(sec, 60.0)
    time = string+' time:  '+str(int(mins))+'min '+str(int(sec))+'s'
    print(time)
    
    return time