from typing import Tuple
from typing import Union
import optuna
with optuna._imports.try_import() as _imports:
import chainer
from chainer.training.extension import Extension
from chainer.training.triggers import IntervalTrigger
from chainer.training.triggers import ManualScheduleTrigger
if not _imports.is_successful():
Extension = object # type: ignore # NOQA
[docs]class ChainerPruningExtension(Extension):
"""Chainer extension to prune unpromising trials.
See `the example <https://github.com/optuna/optuna-examples/blob/main/
chainer/chainer_integration.py>`__
if you want to add a pruning extension which observes validation
accuracy of a `Chainer Trainer <https://docs.chainer.org/en/stable/
reference/generated/chainer.training.Trainer.html>`_.
Args:
trial:
A :class:`~optuna.trial.Trial` corresponding to the current evaluation of the
objective function.
observation_key:
An evaluation metric for pruning, e.g., ``main/loss`` and
``validation/main/accuracy``. Please refer to
`chainer.Reporter reference <https://docs.chainer.org/en/stable/reference/
util/generated/chainer.Reporter.html>`_ for further details.
pruner_trigger:
A trigger to execute pruning. ``pruner_trigger`` is an instance of
`IntervalTrigger <https://docs.chainer.org/en/stable/reference/generated/
chainer.training.triggers.IntervalTrigger.html>`_ or
`ManualScheduleTrigger <https://docs.chainer.org/en/stable/reference/generated/
chainer.training.triggers.ManualScheduleTrigger.html>`_. `IntervalTrigger <https://
docs.chainer.org/en/stable/reference/generated/chainer.training.triggers.
IntervalTrigger.html>`_ can be specified by a tuple of the interval length and its
unit like ``(1, 'epoch')``.
"""
def __init__(
self,
trial: optuna.trial.Trial,
observation_key: str,
pruner_trigger: Union[Tuple[(int, str)], "IntervalTrigger", "ManualScheduleTrigger"],
) -> None:
_imports.check()
self._trial = trial
self._observation_key = observation_key
self._pruner_trigger = chainer.training.get_trigger(pruner_trigger) # type: ignore
if not isinstance(self._pruner_trigger, (IntervalTrigger, ManualScheduleTrigger)):
pruner_type = type(self._pruner_trigger)
raise TypeError(
"Invalid trigger class: " + str(pruner_type) + "\n"
"Pruner trigger is supposed to be an instance of "
"IntervalTrigger or ManualScheduleTrigger."
)
@staticmethod
def _get_float_value(observation_value: Union[float, "chainer.Variable"]) -> float:
_imports.check()
try:
if isinstance(observation_value, chainer.Variable):
return float(observation_value.data) # type: ignore
else:
return float(observation_value)
except TypeError:
raise TypeError(
"Type of observation value is not supported by ChainerPruningExtension.\n"
"{} cannot be cast to float.".format(type(observation_value))
) from None
def _observation_exists(self, trainer: "chainer.training.Trainer") -> bool:
return self._pruner_trigger(trainer) and self._observation_key in trainer.observation
def __call__(self, trainer: "chainer.training.Trainer") -> None:
if not self._observation_exists(trainer):
return
current_score = self._get_float_value(trainer.observation[self._observation_key])
current_step = getattr(trainer.updater, self._pruner_trigger.unit)
self._trial.report(current_score, step=current_step)
if self._trial.should_prune():
message = "Trial was pruned at {} {}.".format(self._pruner_trigger.unit, current_step)
raise optuna.TrialPruned(message)