def extract_yyyy_mm_dd_hh_mm_ss_from_datetime64(dt64):
    """

    Extract separate fields for year, monday, day, hour, min, sec from
    a datetime64 object
    
    Parameters
    ----------    
    dt64 : numpy.datetime64 
        a datetime64 object

    Returns 
    -------    
    year, mon, day, hh, mm, ss : int

    """
    
    s = str(dt64)
    year = int(s[0:4])
    mon = int(s[5:7])
    day = int(s[8:10])
    hh = int(s[11:13])
    mm = int(s[14:16])
    ss = int(s[17:18])
    
    #print year, mon, day, hh, mm, ss
    return year,mon,day,hh,mm,ss