def _parse_exon(o):
    """Parse exon information from an Ensembl `overlap` query.

    :param o: A Python dict representing an entry from the response.
    :type o: dict

    :returns: A tuple of (start, end) positions representing the exon.
    :rtype: tuple

    """
    assert o['feature_type'] == 'exon'
    return o['start'], o['end']
