Concise and precise relative datetime

relative_datetime.py

def relative_datetime(then):
    delta = arrow.now() - then
    
    years, days_of_year = delta.days // 365, delta.days % 365
    months_of_year, days_of_month = days_of_year // 30, days_of_year % 30
    
    hours_of_day, seconds_of_hour = delta.seconds // (60*60), delta.seconds % (60*60)
    minutes_of_hour, seconds_of_minute = seconds_of_hour // 60, seconds_of_hour % 60
    
    if years != 0:
        return      "%dy" % years if months_of_year == 0 \
               else "%dy %dm" % (years, months_of_year)
    
    elif months_of_year != 0:
        return      "%dm" % months_of_year if days_of_month == 0 \
               else "%dm %dd" % (months_of_year, days_of_month)
    
    elif days_of_month != 0:
        return      "%dd" % days_of_month if hours_of_day == 0 \
               else "%dd %dh" % (days_of_month, hours_of_day)
               
    elif hours_of_day != 0:
        return      "%dh" % hours_of_day if minutes_of_hour == 0 \
               else "%dh %dm" % (hours_of_day, minutes_of_hour)
       
    elif minutes_of_hour != 0:
        return "%dm" % minutes_of_hour
    
    else:
        return "just now"