helios.plugins.optuna
=====================

.. py:module:: helios.plugins.optuna


Classes
-------

.. autoapisummary::

   helios.plugins.optuna.OptunaPlugin


Module Contents
---------------

.. py:class:: OptunaPlugin(trial: optuna.Trial, metric_name: str)

   Bases: :py:obj:`helios.plugins.Plugin`


   Plug-in to do hyper-parameter tuning with Optuna.

   This plug-in integrates `Optuna <https://optuna.readthedocs.io/en/stable/>`__ into the
   training system in order to provide hyper-parameter tuning. The plug-in provides the
   following functionality:

   #. Automatic handling of trial pruning.
   #. Automatic reporting of metrics.
   #. Exception registration for trial pruning.
   #. Easy integration with Helios' checkpoint system to continue stopped trials.

   .. warning::
       This plug-in **requires** Optuna to be installed before being used. If it isn't,
       then :py:exc:`ImportError` is raised.

   .. rubric:: Example

   .. code-block:: python

       import helios.plugins as hlp
       import optuna

       def objective(trial: optuna.Trial) -> float:
           datamodule = ...
           model = ...
           plugin = hlp.optuna.OptunaPlugin(trial, "accuracy")

           trainer = ...

           # Automatically registers the plug-in with the trainer.
           plugin.configure_trainer(trainer)

           # This can be skipped if you don't want the auto-resume functionality or
           # if you wish to manage it yourself.
           plugin.configure_model(model)

           trainer.fit(model, datamodule)
           plugin.check_pruned()
           return model.metrics["accuracy"]

       def main():
           # Note that the plug-in requires the storage to be persistent.
           study = optuna.create_study(storage="sqlite:///example.db", ...)
           study.optimize(objective, ...)

   :param trial: the Optuna trial.
   :param metric_name: the name of the metric to monitor. This assumes the name will be
                       present in the :py:attr:`~helios.model.model.Model.metrics` table.


   .. py:attribute:: plugin_id
      :value: 'optuna'



   .. py:property:: trial
      :type: optuna.Trial

      Return the trial.


   .. py:method:: configure_trainer(trainer: helios.trainer.Trainer) -> None

      Configure the trainer with the required settings.

      This will do two things:

      #. Register the plug-in itself with the trainer.
      #. Append the trial pruned exception to the trainer.

      :param trainer: the trainer instance.



   .. py:method:: configure_model(model: helios.model.Model) -> None

      Configure the model to allow trials to resume.

      This will alter the :py:attr:`~helios.model.model.Model.save_name` property of the
      model by appending :code:`_trial-<trial-numer>`. In the event that a trial with
      that number has already been attempted, it will be set to that number instead.
      This will allow the automatic checkpoint system of the trainer to resume the
      trial.

      :param model: the model instance.



   .. py:method:: suggest(type_name: str, name: str, **kwargs: Any) -> Any

      Generically Wrap the ``suggest_`` family of functions of the optuna trial.

      This function can be used to easily invoke the corresponding ``suggest_`` function
      from the Optuna trial held by the plug-in without having to manually type each
      individual function. This lets you write generic code that can be controlled by an
      external source (such as command line arguments or a config table). The function
      wraps the following functions:

      .. list-table:: Suggestion Functions
          :header-rows: 1

          * - Function
            - Name
          * - ``optuna.Trial.suggest_categorical``
            - categorical
          * - ``optuna.Trial.suggest_int``
            - int
          * - ``optuna.Trial.suggest_float``
            - float

      .. warning::
          Functions that are marked as deprecated by Optuna are *not* included in this
          wrapper.

      .. note::
          You can find the exact arguments for each function `here
          <https://optuna.readthedocs.io/en/stable/reference/generated/optuna.trial.Trial.html>`__.

      .. rubric:: Example

      .. code-block:: python

          import helios.plugin as hlp
          import optuna

          def objective(trial: optuna.Trial) -> float:
              plugin = hlp.optuna.OptunaPlugin(trial, "accuracy")
              # ... configure model and trainer.

              val1 = plugin.suggest("categorical", "val1", choices=[1, 2, 3])
              val2 = plugin.suggest("int", "val2", low=0, high=10)
              val3 = plugin.suggest("float", "val3", low=0, high=1)

      :param type_name: the name of the type to suggest from.
      :param name: a parameter name
      :param \*\*kwargs: keyword arguments to the corresponding suggest function.

      :raises KeyError: if the value passed in to ``type_name`` is not recognised.



   .. py:method:: setup() -> None

      Configure the plug-in.

      :raises ValueError: if the study wasn't created with persistent storage.



   .. py:method:: on_validation_end(validation_cycle: int) -> None

      Report metrics to the trial.

      .. note::
          In distributed training, only rank 0 will report the metrics to the trial.

      :param validation_cycle: the current validation cycle.



   .. py:method:: should_training_stop() -> bool

      Handle trial pruning.

      :returns: True if the trial should be pruned, false otherwise.



   .. py:method:: on_training_end() -> None

      Clean-up on training end.

      If training is non-distributed and the trial was pruned, then this function will
      do the following:

      #. Call :py:meth:`~helios.model.model.Model.on_training_end` to ensure metrics are
         correctly logged (if using).
      #. Raise :py:exc:`optuna.TrialPruned` exception to signal the trial was pruned.

      If training is distributed, this function does nothing.

      :raises TrialPruned: if the trial was pruned.



   .. py:method:: check_pruned() -> None

      Ensure pruned distributed trials are correctly handled.

      Due to the way distributed training works, we can't raise an exception within the
      distributed processes, so we have to do it after we return to the main process.
      If the trial was pruned, this function will raise :py:exc:`optuna.TrialPruned`. If
      distributed training wasn't used, this function does nothing.

      .. warning::
          You *must* ensure this function is called after
          :py:meth:`~helios.trainer.Trainer.fit` to ensure pruning works correctly.

      :raises TrialPruned: if the trial was pruned.