code: def _compute_enlarge_labels(self, locator, base_index):
          
          # base_index_type can be pd.Index or pd.DatetimeIndex
          # depending on user input and pandas behavior
          # See issue #2264
          base_index_type = type(base_index)
          locator_as_index = base_index_type(locator)
  
          nan_labels = locator_as_index.difference(base_index)
          common_labels = locator_as_index.intersection(base_index)
  
          if len(common_labels) == 0:
              raise KeyError(
                  "None of [{labels}] are in the [{base_index_name}]".format(
                      labels=list(locator_as_index), base_index_name=base_index
                  )
              )
          return nan_labels
docs: Helper for _enlarge_axis, compute common labels and extra labels.
  
          Returns:
               nan_labels: The labels needs to be added