code: def lookup_path(self, mold_id_path, default=_marker):
          
  
          fragments = mold_id_path.split('/')
          mold_id = '/'.join(fragments[:2])
          try:
              subpath = []
              for piece in fragments[2:]:
                  if (sep in piece or (altsep and altsep in piece) or
                          piece == pardir):
                      raise KeyError
                  elif piece and piece != '.':
                      subpath.append(piece)
              path = self.mold_id_to_path(mold_id)
          except KeyError:
              if default is _marker:
                  raise
              return default
  
          return join(path, *subpath)
docs: For the given mold_id_path, look up the mold_id and translate
          that path to its filesystem equivalent.