docs: def set_extension(self, ext):
          """
          RETURN NEW FILE WITH GIVEN EXTENSION
          """
          path = self._filename.split("/")
          parts = path[-1].split(".")
          if len(parts) == 1:
              parts.append(ext)
          else:
              parts[-1] = ext
  
          path[-1] = ".".join(parts)
          return File("/".join(path))