code: def cover(self, match_set):
          
  
          assert isinstance(match_set, MatchSet)
          assert match_set.model.algorithm is self
  
          # Create a new condition that matches the situation.
          condition = bitstrings.BitCondition.cover(
              match_set.situation,
              self.wildcard_probability
          )
  
          # Pick a random action that (preferably) isn't already suggested by
          # some other rule for this situation.
          action_candidates = (
              frozenset(match_set.model.possible_actions) -
              frozenset(match_set)
          )
          if not action_candidates:
              action_candidates = match_set.model.possible_actions
          action = random.choice(list(action_candidates))
  
          # Create the new rule.
          return XCSClassifierRule(
              condition,
              action,
              self,
              match_set.time_stamp
          )
docs: Return a new classifier rule that can be added to the match set,
          with a condition that matches the situation of the match set and an
          action selected to avoid duplication of the actions already
          contained therein. The match_set argument is a MatchSet instance
          representing the match set to which the returned rule may be added.
  
          Usage:
              match_set = model.match(situation)
              if model.algorithm.covering_is_required(match_set):
                  new_rule = model.algorithm.cover(match_set)
                  assert new_rule.condition(situation)
                  model.add(new_rule)
                  match_set = model.match(situation)
  
          Arguments:
              match_set: A MatchSet instance.
          Return:
              A new ClassifierRule instance, appropriate for the addition to
              match_set and to the classifier set from which match_set was
              drawn.