code: def has_index(self, index):
          
          klass = index if isclass(index) else index.__class__
          for one_index in self._indexes:
              if isinstance(one_index, klass):
                  return True
          return False
docs: Tells if the field have an index matching the current one
  
          Parameters
          -----------
          index: type or BaseIndex
              It could be an index instance, or an index class
  
          Returns
          -------
          bool
              Will be ``True`` if the current field has an index that is an instance
              of the given index or of the class of the given index