code: def scalars_impl(self, run, tag_regex_string):
      
      if not tag_regex_string:
        # The user provided no regex.
        return {
            _REGEX_VALID_PROPERTY: False,
            _TAG_TO_EVENTS_PROPERTY: {},
        }
  
      # Construct the regex.
      try:
        regex = re.compile(tag_regex_string)
      except re.error:
        return {
            _REGEX_VALID_PROPERTY: False,
            _TAG_TO_EVENTS_PROPERTY: {},
        }
  
      # Fetch the tags for the run. Filter for tags that match the regex.
      run_to_data = self._multiplexer.PluginRunToTagToContent(
          scalars_metadata.PLUGIN_NAME)
  
      tag_to_data = None
      try:
        tag_to_data = run_to_data[run]
      except KeyError:
        # The run could not be found. Perhaps a configuration specified a run that
        # TensorBoard has not read from disk yet.
        payload = {}
  
      if tag_to_data:
        scalars_plugin_instance = self._get_scalars_plugin()
        if not scalars_plugin_instance:
          raise ValueError(('Failed to respond to request for /scalars. '
                            'The scalars plugin is oddly not registered.'))
  
        form = scalars_plugin.OutputFormat.JSON
        payload = {
          tag: scalars_plugin_instance.scalars_impl(tag, run, None, form)[0]
              for tag in tag_to_data.keys()
              if regex.match(tag)
        }
  
      return {
          _REGEX_VALID_PROPERTY: True,
          _TAG_TO_EVENTS_PROPERTY: payload,
      }
docs: Given a tag regex and single run, return ScalarEvents.
  
      Args:
        run: A run string.
        tag_regex_string: A regular expression that captures portions of tags.
  
      Raises:
        ValueError: if the scalars plugin is not registered.
  
      Returns:
        A dictionary that is the JSON-able response.