def getUsers(context, roles, allow_empty=True):
    """ Present a DisplayList containing users in the specified
        list of roles
    """
    mtool = getToolByName(context, 'portal_membership')
    pairs = allow_empty and [['', '']] or []
    users = mtool.searchForMembers(roles=roles)
    for user in users:
        uid = user.getId()
        fullname = user.getProperty('fullname')
        if not fullname:
            fullname = uid
        pairs.append((uid, fullname))
    pairs.sort(lambda x, y: cmp(x[1], y[1]))
    return DisplayList(pairs)
Present a DisplayList containing users in the specified
        list of roles