Promote _Segments, _Segment, _Chunk to public API

[bessman]

It would be nice to be able to use these types in annotations:

write_data(data: bincopy.Chunk) -> None:
    ...

instead of having to write:

write_data(data: bincopy._Segment._Chunk) -> None:
    ...

which is both harder on the eyes and makes various linters complain about accessing protected members.

[eerimoq]

Good suggestion (probably). Part of version 18.0.0.

[eerimoq]

In case this breaks peoples code, I could add aliases like _Segments = Segments. I think I'll do that actually.

[bessman]

Great! Here's another, related suggestion: Segment.chunks should yield smaller Segments instead of Chunks.

My use case is that I need to split a Segment into chunks for writing to a target device. Then I need to split those chunks into smaller chunks in order to calculate a checksum of the larger chunk. But Chunk doesn't have a .chunks method, so that doesn't work :(

Instead, I created a new Segment and chunked that:

Segment(chunk.address, chunk.address + len(chunk.data), chunk.data, 1).chunks()

But is there any reason chunks can't just yield Segments to begin with?

[eerimoq]

Not that I can think of, but was some time I used bincopy so I might have forgotten. If you have time you could submit a PR with the change and I can have a closer look (and maybe you encounter some problem).

[bessman]

Segment._word_size_bytes should have a public getter. It is useful to be able to get chunks of a certain number of bytes, for example when calculating a checksum. Since .chunks wants the size and alignment in words, it is necessary to know the word size to get a certain number of bytes per chunk. The Segment knows it internally, but it's only public on the BinFile, which may not be available in a subroutine.

[eerimoq]

Feel free to make it public on Segment as well.