class_docstr: An abstract base class for implementing explainer algorithms.
docstr: Determines the message passing flow of the :obj:`model`.
docstr_tok: ["Determines","the","message","passing","flow","of","the",":","obj",":","`","model","`","."]
code: def _flow(model: torch.nn.Module) -> str:
      r"""Determines the message passing flow of the :obj:`model`."""
      for module in model.modules():
          if isinstance(module, MessagePassing):
              return module.flow
      return "source_to_target"
  
imports: from abc import abstractmethod
  from typing import Dict, Optional, Tuple, Union
  import torch
  import torch.nn.functional
  from torch import Tensor
  from torch_geometric.explain import Explanation, HeteroExplanation
  from torch_geometric.explain.config import ExplainerConfig, ModelConfig, ModelReturnType
  from torch_geometric.nn import MessagePassing
  from torch_geometric.typing import EdgeType, NodeType
  from torch_geometric.utils import k_hop_subgraph
label_desc: Use image node_id 9 for calling the ExplainerAlgorithm obj's underlying member method code with example usage: obj._flow(model) and returns: str, module