Switch `FileLoader` to `FileOpener`

Should we change the name of FileLoader to FileOpener?

We split the file-loading functionality into three steps:

• List file names in a directory: FileLister
• Open file handles: FileLoader (I personally feel like the name is incorrect.)
• Read files: dp.map(fn=lambda x: x.read(), input_col=1)

cc: @VitalyFedyunin @NivekT

[NivekT]

From a purely naming perspective, I think FileOpener is more accurate but FileLoader isn’t wildly misleading either.

I had a look at numpy.load, json.load, pickle.load, these seem to either read or parse through files that have already been opened and return some structured data. In that sense, FileLoader definitely behaves differently relative to other modules. Renaming it is likely better.

Perhaps we can rename it, but still leave FileLoader functional with a deprecation warning? I would imagine most people who started using IterDataPipe in PyTorch Core would be using FileLoader and it would be a BC-breaking change.

[NivekT]

I agree that based on the prototyping policy we should be able to rename as we wish. I think the policy is very clear for things that exist in TorchData. Do you think that policy is clear to users for things that are in PyTorch Core? If so, then we can rename it without deprecation.