Set the timezone for datetime fields.
    By default is your machine's time.
    If it's called without parameter sets the
    local time again.

    :keyword param new_tz: timezone string
    ex. 'Europe/Athens',
        'Asia/Seoul',
        'America/Los_Angeles',
        'UTC'

    :return
        None

def set_timezone(new_tz=None):
    """Set the timezone for datetime fields.
    By default is your machine's time.
    If it's called without parameter sets the
    local time again.

    :keyword param new_tz: timezone string
    ex. 'Europe/Athens',
        'Asia/Seoul',
        'America/Los_Angeles',
        'UTC'

    :return
        None
    """
    global tz
    if new_tz:
        tz = pytz.timezone(new_tz)
    else:
        tz = tzlocal.get_localzone()