class_docstr: Visitor to produce a human readable string for a graph.
code: def get_dot_graph(self) -> pydot.Dot:
      return self._dot_graph
  
imports: import abc
  import collections
  import dataclasses
  from typing import Any, Collection, Dict, List, Optional, Tuple
  import pydot
label_desc: Use image node_id 2 for calling the _PrintGraphVisitor obj's underlying member method code with example usage: obj.get_dot_graph() and returns: self