| # Copyright (c) 2025, NVIDIA CORPORATION. All rights reserved. | |
| # | |
| # 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 | |
| # distributed under the License is distributed on an "AS IS" BASIS, | |
| # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| # See the License for the specific language governing permissions and | |
| # limitations under the License. | |
| import torch | |
| from nemo.utils import logging | |
| class FallbackDataset(torch.utils.data.Dataset): | |
| """ | |
| FallbackDataset is a wrapper on an existing map-style ``torch.utils.data.Dataset``. | |
| It's used to return the previous item (or batch, depending on Dataset) whenever | |
| the underlying ``Dataset`` returns ``None``. | |
| This is useful when ``Dataset`` returns a full batch (as e.g. Lhotse datasets typically do), | |
| and wasn't able to read any of the items in that batch. | |
| Example:: | |
| >>> dataset = AudioToTextLhotseDataset(...) | |
| ... dataset = FallbackDataset(dataset) | |
| """ | |
| def __init__(self, dataset): | |
| self.dataset = dataset | |
| self._fallback = None | |
| def __getitem__(self, item): | |
| ans = self.dataset[item] | |
| if ans is None: | |
| if self._fallback is None: | |
| logging.warning( | |
| f"FallbackDataset received None from {self.dataset} on the first call to __getitem__, " | |
| f"and must return None instead of an actual batch." | |
| f"This indicates an issue with data reading." | |
| ) | |
| ans = self._fallback | |
| self._fallback = ans | |
| return ans | |
| def __len__(self): | |
| return len(self.dataset) | |