code: def getUsers(context, roles, allow_empty=True):
      
      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)
docs: Present a DisplayList containing users in the specified
          list of roles