code: def get_edge_direction_and_name(vertex_field_name):
      
      edge_direction = None
      edge_name = None
      if vertex_field_name.startswith(OUTBOUND_EDGE_FIELD_PREFIX):
          edge_direction = OUTBOUND_EDGE_DIRECTION
          edge_name = vertex_field_name[len(OUTBOUND_EDGE_FIELD_PREFIX):]
      elif vertex_field_name.startswith(INBOUND_EDGE_FIELD_PREFIX):
          edge_direction = INBOUND_EDGE_DIRECTION
          edge_name = vertex_field_name[len(INBOUND_EDGE_FIELD_PREFIX):]
      else:
          raise AssertionError(u'Unreachable condition reached:', vertex_field_name)
  
      validate_safe_string(edge_name)
  
      return edge_direction, edge_name
docs: Get the edge direction and name from a non-root vertex field name.