def parse_evidence(evidence):
    """
    From an evidence string/element return a dictionary or obs/counts

    Updated where to handle 0 coverage in an 'N' call! In this case we set
    N = -1

    :param evidence: an evidence string. It looks something like this -
                        Ax27 AGCAx1 AGCAATTAATTAAAATAAx
    """
    obs_count = {}
    elem = evidence.split(' ')
    if elem == ['']:
        obs_count['N'] = -1
    else:
        for e in elem:
            obs, count = e.split('x')
            obs_count[obs] = int(count)
    return obs_count