code: def parse_spec(self, spec):
      
  
      if spec.endswith('::'):
        spec_path = spec[:-len('::')]
        return DescendantAddresses(self._normalize_spec_path(spec_path))
      elif spec.endswith(':'):
        spec_path = spec[:-len(':')]
        return SiblingAddresses(self._normalize_spec_path(spec_path))
      else:
        spec_parts = spec.rsplit(':', 1)
        spec_path = self._normalize_spec_path(spec_parts[0]) 
        name = spec_parts[1] if len(spec_parts) > 1 else os.path.basename(spec_path)
        return SingleAddress(spec_path, name)
docs: Parse the given spec into a `specs.Spec` object.
  
      :param spec: a single spec string.
      :return: a single specs.Specs object.
      :raises: CmdLineSpecParser.BadSpecError if the address selector could not be parsed.