class_docstr: Generates a motif based on a custom structure coming from a
  :class:`torch_geometric.data.Data` or :class:`networkx.Graph` object.
  
  Args:
      structure (torch_geometric.data.Data or networkx.Graph): The structure
          to use as a motif.
code: def __call__(self) -> Data:
      assert isinstance(self.structure, Data)
      return self.structure
  
imports: from typing import Any, Optional
  from torch_geometric.data import Data
  from torch_geometric.datasets.motif_generator import MotifGenerator
  from torch_geometric.utils import from_networkx
label_desc: Use image node_id 2 for calling the CustomMotif obj's underlying member method code with example usage: obj.__call__() and returns: self