Fastai

New Features

- Option to preserve filenames in `download_images` ([2983](https://github.com/fastai/fastai/pull/2983)), thanks to [mess-lelouch](https://github.com/mess-lelouch)
- Deprecate `config` in `create_cnn` and instead pass kwargs directly ([2966](https://github.com/fastai/fastai/pull/2966)), thanks to [borisdayma](https://github.com/borisdayma)

Bugs Squashed

- Progress and Recorder callbacks serialize their data, resulting in large Learner export file sizes ([2981](https://github.com/fastai/fastai/issues/2981))
- `TextDataLoaders.from_df()` returns `TypeError: 'float' object is not iterable` ([2978](https://github.com/fastai/fastai/issues/2978))
- "only one element tensors can be converted to Python scalars" exception in Siamese Tutorial ([2973](https://github.com/fastai/fastai/issues/2973))
- Learn.load and LRFinder not functioning properly for the optimizer states ([2892](https://github.com/fastai/fastai/issues/2892))

Breaking Changes

- remove `log_args` ([2954](https://github.com/fastai/fastai/issues/2954))

New Features

- Improve performance of `RandomSplitter` (h/t muellerzr) ([2957](https://github.com/fastai/fastai/issues/2957))

Bugs Squashed

- Exporting TabularLearner via learn.export() leads to huge file size ([2945](https://github.com/fastai/fastai/issues/2945))
- `TensorPoint` object has no attribute `img_size` ([2950](https://github.com/fastai/fastai/issues/2950))

Breaking Changes

- moved `has_children` from `nn.Module` to free function ([2931](https://github.com/fastai/fastai/issues/2931))

New Features

- Support persistent workers ([2768](https://github.com/fastai/fastai/issues/2768))

Bugs Squashed

- `unet_learner` segmentation fails ([2939](https://github.com/fastai/fastai/issues/2939))
- In "Transfer learning in text" tutorial, the "dls.show_batch()" show wrong outputs ([2910](https://github.com/fastai/fastai/issues/2910))
- `Learn.load` and `LRFinder` not functioning properly for the optimizer states ([2892](https://github.com/fastai/fastai/issues/2892))
- Documentation for `Show_Images` broken ([2876](https://github.com/fastai/fastai/issues/2876))
- URL link for documentation for `torch_core` library from the `doc()` method gives incorrect url ([2872](https://github.com/fastai/fastai/issues/2872))

Bugs Squashed

- Work around broken PyTorch subclassing of some `new_*` methods ([2769](https://github.com/fastai/fastai/issues/2769))

New Features

- PyTorch 1.7 compatibility ([2917](https://github.com/fastai/fastai/issues/2917))

PyTorch 1.7 includes support for tensor subclassing, so we have replaced much of our custom subclassing code with PyTorch's. We have seen a few bugs in PyTorch's subclassing feature, however, so please file an issue if you see any code failing now which was working before.

There is one breaking change in this version of fastai, which is that custom metadata is now stored directly in tensors as standard python attributes, instead of in the special `_meta` attribute. Only advanced customization of fastai OO tensors would have used this functionality, so if you do not know what this all means, then it means you did not use it.

This version was released *after* `2.1.0`, and adds fastcore 1.3 compatibility, whilst maintaining PyTorch 1.6 compatibility. It has no new features or bug fixes.