Refactor the sequence interface

[mgeier]

Refactoring:

• factor-out duplicate code to separate method _get_slice_bounds()
• replace 4 if-clauses with one call to slice.indices()
  • issue sequence interface: off-by-one error #6 is still not solved because len() is still broken (off-by-one error in __len__() #11)

Change behavior to be more sane:

• raise error if step != 1
  • this was silently ignored before

Change behavior to be closer to Python indexing:

• if start > stop (assuming step==1), an empty array is returned
  • before, the two values were flipped
• if negative values exceed length, they are set to maximum
  • something strange happened before ...

[bastibe]

Very nice! Thank you so much for this contribution!
I didn't know about the slice.indices method. That is very useful!

If I understand your commit correctly, you disallow steps that are greater than 1. This seems to mean that I can't SoundFile('file')[100:1000] any more. Is that correct? I would definitely want to allow that.

In fact, I wanted to extend the index operator to channel selections. I would love to be able to SoundFile('file')[0, :44100] to get the first second of the first channel.

[mgeier]

Your example should still work, "step" is the third argument to the slice.

This would not work: SoundFile('file')[100:1000:2]. In the current version, the third argument is just silently ignored, which is not what I would expect.
I simply created an error message for this case.

In the future it would of course be nice to support a step size (for whatever reason this should be needed ...), but this needs a bit more work.
And then, of course, my error message must be removed again.

And I would also like to have the 2-dimensional indexing, this would have been one of my next questions ...
Are you planning to work on it or shall I give it a try?

[bastibe]

Oh, I get it now. Yes, that is perfect!

I am currently pretty short on time, so if you want to give 2-dimensional indexing a shot, I'd be very grateful! I will merge your many contributions tomorrow and recut the binaries. I actually managed to reserve a solid few hours solely for PySoundFile and PySoundCard tomorrow.

[mgeier]

Thanks for merging!

I created an issue for 2D indexing: #15.