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: Initialization.
code: def __init__(self):
      """Initialization."""
      self._context = {}
  
file_path: MatchZoo/matchzoo/preprocessors/units/stateful_unit.py
imports: import abc
  import typing
  from .unit import Unit
label_desc: Use image node_id 1 to create a new StatefulUnit object from inherited base classes: Unit with example: obj = StatefulUnit()