Source code for monai.handlers.checkpoint_loader

# 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, Dict, Optional

import torch

from monai.utils import exact_version, optional_import

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


[docs]class CheckpointLoader: """ CheckpointLoader acts as an Ignite handler to load checkpoint data from file. It can load variables for network, optimizer, lr_scheduler, etc. If saving checkpoint after `torch.nn.DataParallel`, need to save `model.module` instead as PyTorch recommended and then use this loader to load the model. Args: load_path: the file path of checkpoint, it should be a PyTorch `pth` file. load_dict: target objects that load checkpoint to. examples:: {'network': net, 'optimizer': optimizer, 'lr_scheduler': lr_scheduler} name: identifier of logging.logger to use, if None, defaulting to ``engine.logger``. map_location: when loading the module for distributed training/evaluation, need to provide an appropriate map_location argument to prevent a process to step into others’ devices. If map_location is missing, torch.load will first load the module to CPU and then copy each parameter to where it was saved, which would result in all processes on the same machine using the same set of devices. """ def __init__( self, load_path: str, load_dict: Dict, name: Optional[str] = None, map_location: Optional[Dict] = None, ) -> None: if load_path is None: raise AssertionError("must provide clear path to load checkpoint.") self.load_path = load_path if not (load_dict is not None and len(load_dict) > 0): raise AssertionError("must provide target objects to load.") self.logger = logging.getLogger(name) self.load_dict = load_dict self._name = name self.map_location = map_location
[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 engine.add_event_handler(Events.STARTED, self)
def __call__(self, engine: Engine) -> None: """ Args: engine: Ignite Engine, it can be a trainer, validator or evaluator. """ checkpoint = torch.load(self.load_path, map_location=self.map_location) Checkpoint.load_objects(to_load=self.load_dict, checkpoint=checkpoint) self.logger.info(f"Restored all variables from {self.load_path}")