input :
    date : date type
    local_tz : bool

    offset generated from _calculate_offset
    offset in seconds
    offset = 0 -> +00:00
    offset = 1800 -> +00:30
    offset = -3600 -> -01:00

def _generate_timezone(date, local_tz):
    """
    input :
    date : date type
    local_tz : bool

    offset generated from _calculate_offset
    offset in seconds
    offset = 0 -> +00:00
    offset = 1800 -> +00:30
    offset = -3600 -> -01:00
    """
    offset = _calculate_offset(date, local_tz)

    hour = abs(offset) // 3600
    minute = abs(offset) % 3600 // 60

    if offset < 0:
        return '%c%02d:%02d' % ("-", hour, minute)
    else:
        return '%c%02d:%02d' % ("+", hour, minute)