class_docstr: Base class for NAS strategies.
  
  To explore a space with a strategy, use::
  
      strategy = MyStrategy()
      strategy(model_space, engine)
  
  The strategy has a :meth:`run` method, that defines the process of exploring a NAS space.
  
  Strategy is stateful. It might store information of the current :meth:`initialize` and :meth:`run` as member attributes.
  We do not allow :meth:`run` a strategy twice with same, or different model spaces.
  
  Subclass should override :meth:`_initialize` and :meth:`_run`,
  as well as :meth:`state_dict` and :meth:`load_state_dict` for checkpointing.
class_docstr_tok: ["Base","class","for","NAS","strategies",".","To","explore","a","space","with","a","strategy",",","use",":",":","strategy","=","MyStrategy","(",")","strategy","(","model_space",",","engine",")","The","strategy","has","a",":","meth",":","`","run","`","method",",","that","defines","the","process","of","exploring","a","NAS","space",".","Strategy","is","stateful",".","It","might","store","information","of","the","current",":","meth",":","`","initialize","`","and",":","meth",":","`","run","`","as","member","attributes",".","We","do","not","allow",":","meth",":","`","run","`","a","strategy","twice","with","same",",","or","different","model","spaces",".","Subclass","should","override",":","meth",":","`","_initialize","`","and",":","meth",":","`","_run","`",",","as","well","as",":","meth",":","`","state_dict","`","and",":","meth",":","`","load_state_dict","`","for","checkpointing","."]
code: def __init__(
      self,
      model_space: ExecutableModelSpace | None = None,
      engine: ExecutionEngine | None = None,
  ):
      self._engine: ExecutionEngine | None = None
      self._model_space: ExecutableModelSpace | None = None
  
      # Status is internal for now.
      self._status = StrategyStatus.EMPTY
      if engine is not None and model_space is not None:
          self.initialize(model_space, engine)
      elif engine is not None or model_space is not None:
          raise ValueError(
              "Both engine and model_space should be provided, or both should be None."
          )
  
imports: from __future__ import annotations
  import logging
  import time
  from enum import Enum
  from typing import Iterator, cast
  from nni.nas.execution import ExecutionEngine
  from nni.nas.space import ExecutableModelSpace, ModelStatus
  from nni.typehint import TrialMetric
label_desc: Use image node_id 1 to create a new Strategy object  with example: obj = Strategy(model_space, engine)