Source code for monai.handlers.lr_schedule_handler

# Copyright 2020 - 2021 MONAI Consortium
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#     http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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import logging
from typing import TYPE_CHECKING, Any, Callable, Optional, Union

from torch.optim.lr_scheduler import ReduceLROnPlateau, _LRScheduler

from monai.utils import ensure_tuple, exact_version, optional_import

Events, _ = optional_import("ignite.engine", "0.4.2", exact_version, "Events")
if TYPE_CHECKING:
    from ignite.engine import Engine
else:
    Engine, _ = optional_import("ignite.engine", "0.4.2", exact_version, "Engine")


[docs]class LrScheduleHandler: """ Ignite handler to update the Learning Rate based on PyTorch LR scheduler. """ def __init__( self, lr_scheduler: Union[_LRScheduler, ReduceLROnPlateau], print_lr: bool = True, name: Optional[str] = None, epoch_level: bool = True, step_transform: Callable[[Engine], Any] = lambda engine: (), ) -> None: """ Args: lr_scheduler: typically, lr_scheduler should be PyTorch lr_scheduler object. If customized version, must have `step` and `get_last_lr` methods. print_lr: whether to print out the latest learning rate with logging. name: identifier of logging.logger to use, if None, defaulting to ``engine.logger``. epoch_level: execute lr_scheduler.step() after every epoch or every iteration. `True` is epoch level, `False` is iteration level. step_transform: a callable that is used to transform the information from `engine` to expected input data of lr_scheduler.step() function if necessary. Raises: TypeError: When ``step_transform`` is not ``callable``. """ self.lr_scheduler = lr_scheduler self.print_lr = print_lr self.logger = logging.getLogger(name) self.epoch_level = epoch_level if not callable(step_transform): raise TypeError(f"step_transform must be callable but is {type(step_transform).__name__}.") self.step_transform = step_transform self._name = name
[docs] def attach(self, engine: Engine) -> None: """ Args: engine: Ignite Engine, it can be a trainer, validator or evaluator. """ if self._name is None: self.logger = engine.logger if self.epoch_level: engine.add_event_handler(Events.EPOCH_COMPLETED, self) else: engine.add_event_handler(Events.ITERATION_COMPLETED, self)
def __call__(self, engine: Engine) -> None: """ Args: engine: Ignite Engine, it can be a trainer, validator or evaluator. """ args = ensure_tuple(self.step_transform(engine)) self.lr_scheduler.step(*args) if self.print_lr: self.logger.info(f"Current learning rate: {self.lr_scheduler._last_lr[0]}") # type: ignore[union-attr]