'Return dict mapping each feedback type to a set of sr id36s.'

@classmethod
def for_user(cls, account):

    feedback = defaultdict(set)
    try:
        row = AccountSRFeedback._cf.get(account._id36, column_count=max_column_count)
    except pycassa.NotFoundException:
        return feedback
    for (colkey, colval) in row.iteritems():
        (action, sr_id36) = colkey.split('.')
        feedback[action].add(sr_id36)
    return feedback
