code: def __str__(self):
      function_expr = None
      for project_expr in self._project_expr_list:
          if isinstance(project_expr, FunctionExpression):
              function_expr = project_expr
  
      return "CreateIndexPlan(name={}, \
              table_ref={}, \
              col_list={}, \
              vector_store_type={}, \
              {})".format(
          self._name,
          self._table_ref,
          tuple(self._col_list),
          self._vector_store_type,
          ""
          if function_expr is None
          else "function={}".format(function_expr),
      )
  
file_path: evadb/evadb/plan_nodes/create_index_plan.py
imports: from typing import List
  from evadb.catalog.catalog_type import VectorStoreType
  from evadb.expression.abstract_expression import AbstractExpression
  from evadb.expression.function_expression import FunctionExpression
  from evadb.parser.create_statement import ColumnDefinition
  from evadb.parser.table_ref import TableRef
  from evadb.plan_nodes.abstract_plan import AbstractPlan
  from evadb.plan_nodes.types import PlanOprType
label_desc: Use image node_id 9 for calling the CreateIndexPlan obj's underlying member method code with example usage: obj.__str__() and returns: str