code: def add(self, dist):
          
          if self.can_add(dist) and dist.has_version():
              dists = self._distmap.setdefault(dist.key, [])
              if dist not in dists:
                  dists.append(dist)
                  dists.sort(key=operator.attrgetter('hashcmp'), reverse=True)
docs: Add `dist` if we ``can_add()`` it and it has not already been added