class_docstr: The definition of an operation.
  
  This class contains all the information needed to run an operation, except
  the number of inputs and their values.  A subclass should document
  
    - How many inputs it expects, and what they should contain.
    - What it outputs, as a function of its inputs.
  
  An OperationDef is just a specification and does not contain the actual
  computation.
docstr: Returns a str representation of the requested field.
docstr_tok: ["Returns","a","str","representation","of","the","requested","field","."]
code: def get_field_str(self, field_name: str) -> str:
      """Returns a str representation of the requested field."""
      return getattr(self, field_name)
  
imports: import abc
  import collections
  import dataclasses
  from typing import Any, Collection, Dict, List, Optional, Tuple
  import pydot
label_desc: Use image node_id 3 for calling the OperationDef obj's underlying member method code with example usage: obj.get_field_str(field_name) and returns: getattr