code: def most_frequent_terms(self, count=0):
          terms = sorted(self._terms.items(), key=lambda i: -i[1])
          terms = tuple(i[0] for i in terms)
          if count == 0:
              return terms
          elif count > 0:
              return terms[:count]
          else:
              raise ValueError(
                  "Only non-negative values are allowed for count of terms.")