class_docstr: Unit with inner state.
  
  Usually need to be fit before transforming. All information gathered in the
  fit phrase will be stored into its `context`.
docstr: Abstract base method, need to be implemented in subclass.
code: def fit(self, input_: typing.Any):
      """Abstract base method, need to be implemented in subclass."""
  
file_path: MatchZoo/matchzoo/preprocessors/units/stateful_unit.py
imports: import abc
  import typing
  from .unit import Unit
label_desc: Use image node_id 4 for calling the StatefulUnit obj's underlying member method code with example usage: obj.fit(input_) without return types