[Tune] Fix Tune search for python 3.14

[pseudo-rnd-thoughts]

Description

In updating the release tests to check Python 3.14, I found

Traceback (most recent call last):
--
  | File "/tmp/ray/session_2026-05-21_07-44-59_419182_2769/runtime_resources/working_dir_files/s3_ray-release-automation-results_working_dirs_tune_scalability_bookkeeping_overhead_aws_pwtghglleu__anyscale_pkg_5362fa14e94acaf695fd9b81bc1cfc3c/workloads/test_bookkeeping_overhead.py", line 43, in <module>
  | main()
  | ~~~~^^
  | File "/tmp/ray/session_2026-05-21_07-44-59_419182_2769/runtime_resources/working_dir_files/s3_ray-release-automation-results_working_dirs_tune_scalability_bookkeeping_overhead_aws_pwtghglleu__anyscale_pkg_5362fa14e94acaf695fd9b81bc1cfc3c/workloads/test_bookkeeping_overhead.py", line 33, in main
  | timed_tune_run(
  | ~~~~~~~~~~~~~~^
  | name="bookkeeping overhead",
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | ...<3 lines>...
  | max_runtime=max_runtime,
  | ^^^^^^^^^^^^^^^^^^^^^^^^
  | )
  | ^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/utils/release_test_util.py", line 153, in timed_tune_run
  | analysis = tune.run(
  | _train,
  | ...<3 lines>...
  | **run_kwargs,
  | )
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/tune.py", line 986, in run
  | runner.step()
  | ~~~~~~~~~~~^^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/execution/tune_controller.py", line 701, in step
  | raise e
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/execution/tune_controller.py", line 698, in step
  | self.checkpoint()
  | ~~~~~~~~~~~~~~~^^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/execution/tune_controller.py", line 352, in checkpoint
  | self._checkpoint_manager.sync_up_experiment_state(
  | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
  | save_fn=self.save_to_dir, force=force, wait=wait
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | )
  | ^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/execution/experiment_state.py", line 167, in sync_up_experiment_state
  | save_fn()
  | ~~~~~~~^^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/execution/tune_controller.py", line 348, in save_to_dir
  | self._search_alg.save_to_dir(driver_staging_path, session_str=self._session_str)
  | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/search/basic_variant.py", line 406, in save_to_dir
  | _atomic_save(
  | ~~~~~~~~~~~~^
  | state=state_dict,
  | ^^^^^^^^^^^^^^^^^
  | ...<2 lines>...
  | tmp_file_name=f"tmp-{file_name}",
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | )
  | ^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/tune/utils/util.py", line 416, in _atomic_save
  | cloudpickle.dump(state, f)
  | ~~~~~~~~~~~~~~~~^^^^^^^^^^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/cloudpickle/cloudpickle.py", line 1526, in dump
  | Pickler(file, protocol=protocol, buffer_callback=buffer_callback).dump(obj)
  | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  | File "/home/ray/anaconda3/lib/python3.14/site-packages/ray/cloudpickle/cloudpickle.py", line 1313, in dump
  | return super().dump(obj)
  | ~~~~~~~~~~~~^^^^^
  | TypeError: cannot pickle 'itertools.chain' object
  | when serializing dict item '_trial_iter'
  | Subprocess return code: 1

Reviewing python 3.14 release notes, https://docs.python.org/3/whatsnew/3.14.html#itertools, pickle support has been explicitly removed from all itertool functions.
To resolve this problem, we can just lazily evaluate _trial_iter as it is updated in next_trial based on _trial_generator

Related

#63270

[gemini-code-assist]

Code Review

This pull request updates the state serialization and restoration logic in python/ray/tune/search/basic_variant.py by excluding _trial_iter from the saved state and resetting it to None in set_state. Feedback was provided regarding set_state, suggesting that _trial_generator should be explicitly cleared before reconstructing the iterator chain to avoid redundant trials and deep nesting of itertools.chain objects when an object is reused.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Reviewed by Cursor Bugbot for commit 438c278. Configure here.}

[TimothySeah]

LGTM, also ran the release test on this PR.