class_docstr: A `DAGRepr` represents a complete DAG.
  
  Args:
      nodes (`Dict[str, NodeRepr]`): All nodes in the dag, which start with _input and end with _output node.
      edges (`Dict[int, List]`): The edges about data queue schema, such as:
                          { 0: {'data': [(a, ColumnType.SCALAR), (b, ColumnType.SCALAR)], 'schema': {'a', SchemaRepr, 'b', SchemaRepr}}
                            1: {'data': [(b, ColumnType.SCALAR), (c, ColumnType.SCALAR)], 'schema': {'b', SchemaRepr, 'c', SchemaRepr}}
                            2: {'data': [(a, ColumnType.SCALAR), (c, ColumnType.SCALAR)], 'schema': {'a', SchemaRepr, 'c', SchemaRepr}}
                          }
      dag_dict(`Dict`): The dag dict.
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code: def get_base_col(nodes: NodeRepr):
      if nodes.iter_info.type == FilterConst.name:
          return nodes.iter_info.param[FilterConst.param.filter_by]
      if nodes.iter_info.type == TimeWindowConst.name:
          return nodes.iter_info.param[
              TimeWindowConst.param.timestamp_col
          ]
      return None
  
imports: import types
  import uuid
  import json
  from copy import deepcopy
  from typing import Dict, Any, Set, List, Tuple, Optional
  from pydantic import BaseModel
  from towhee.runtime.check_utils import check_set, check_node_iter
  from towhee.runtime.node_repr import NodeRepr
  from towhee.runtime.schema_repr import SchemaRepr
  from towhee.runtime.node_config import TowheeConfig
  from towhee.runtime.constants import WindowAllConst, WindowConst, ConcatConst, MapConst, ReduceConst, FilterConst, TimeWindowConst, FlatMapConst, InputConst, OutputConst, OPType
label_desc: Use image node_id 6 for calling the DAGRepr obj's underlying member method code with example usage: obj.get_base_col(nodes) and returns: None, nodes, nodes