def satellites_used(feed):
    """Counts number of satellites used in calculation from total visible satellites
    Arguments:
        feed feed=data_stream.satellites
    Returns:
        total_satellites(int):
        used_satellites (int):
    """
    total_satellites = 0
    used_satellites = 0

    if not isinstance(feed, list):
        return 0, 0

    for satellites in feed:
        total_satellites += 1
        if satellites['used'] is True:
            used_satellites += 1
    return total_satellites, used_satellites