code: def unique_authors(self, limit):
          
          seen = set()
          if limit == 0:
              limit = None
          seen_add = seen.add  # Assign to variable, so not resolved each time
          return [x.author for x in self.sorted_commits[:limit]
                  if not (x.author in seen or seen_add(x.author))]
docs: Unique list of authors, but preserving order.