code: def truncate_most_common(self, truncation_length):
          '''
          Sorts the counter and keeps only the most common items up to
          ``truncation_length`` in place.
          :type truncation_length: int
          '''
          keep_keys = set(v[0] for v in self.most_common(truncation_length))
          for key in self.keys():
              if key not in keep_keys:
                  self.pop(key)