def METHOD_NAME(dt):
    """
    Return POSIX timestamp corresponding to the datetime instance.
    :param dt: datetime (possibly aware)
    :return: seconds since epoch as float
    """
    epoch = datetime(1970, 1, 1, tzinfo=tz.gettz('UTC'))
    if dt.tzinfo is None or dt.tzinfo.utcoffset(dt) is None:
        dt_utc = dt.replace(tzinfo=tz.gettz('UTC'))
    else:
        dt_utc = dt.astimezone(tz.gettz('UTC'))
    return (dt_utc - epoch).total_seconds()