code: def _extract_cols(gd: "GroupedData") -> List[Column]:
      df = gd._df
      return [df[col] for col in df.columns]
  
imports: from pyspark.sql.connect.utils import check_dependencies
  import warnings
  from typing import Any, Dict, List, Sequence, Union, TYPE_CHECKING, Optional, overload, cast
  from pyspark.rdd import PythonEvalType
  from pyspark.sql.group import GroupedData
  from pyspark.sql.pandas.group_ops import PandasCogroupedOps
  from pyspark.sql.types import NumericType
  from pyspark.sql.types import StructType
  import pyspark.sql.connect.plan
  from pyspark.sql.connect.column import Column
  from pyspark.sql.connect.functions.builtin import _invoke_function, col, lit
  from pyspark.errors import PySparkNotImplementedError, PySparkTypeError
label_desc: Use image node_id 4 for calling the PandasCogroupedOps obj's underlying member method code with example usage: obj._extract_cols(gd) and returns: unknown