class_docstr: Subtract operator (used for unit test purposes only).
      
code: def __init__(self):
      super().__init__()
      self.key = ()
  
file_path: towhee/tests/unittests/mock_operators/sub_operator/sub_operator.py
imports: from typing import NamedTuple
  from towhee.operator import Operator, SharedType
label_desc: Use image node_id 1 to create a new SubOperator object from inherited base classes: Operator with example: obj = SubOperator()