Difference in getDigestPointsOnly behavior between robofab.pens.digestPen and fontPens.digestPointPen

[cjchapman]

I see a difference in behavior in the getDigestPointsOnly() method between robofab.pens.digestPen and fontPens.digestPointPen, and just wanted to check if this is expected:

>>> from robofab.pens.digestPen import DigestPointPen
>>> pen = DigestPointPen()
>>> pen.beginPath()
>>> pen.addPoint((10, 10), "move", "True")
>>> pen.getDigestPointsOnly(needSort=False)
((10, 10),)


>>> from fontPens.digestPointPen import DigestPointPen
>>> pen = DigestPointPen()
>>> pen.beginPath()
>>> pen.addPoint((10, 10), "move", "True")
>>> pen.getDigestPointsOnly(needSort=False)
('beginPath', (10, 10))

This lead to the changes in lines 873 and 890 of CheckOutlinesUFO.py in this PR:
https://github.com/adobe-type-tools/afdko/pull/230/files

[cjchapman]

(If this is not expected behavior, I'd be happy to help by working on this issue.)

[typemytype]

this is an part of a bigger issue: we have DigestPointPen, DataPointPen and RecordingPointPen doing the same thing... I guess we have to agree on one implementation instead of 3 very similar things

DataPointPen is, I guess, my mistake... and can be removed

cc @justvanrossum

[justvanrossum]

@typemytype:
I'm trying to look into whether DigestPointPen and RecordingPointPen could be folded together, but there are quite substantial differences. Although a getDigest() method could be added to RecordingPointPen that returns a hashable representation of the complete contour. Not sure how easy it would be to make that representation exactly the same is the current DigestPointPen. Or whether that is important at all. But this very issue seems to say that it may be.

DataPointPen is largely equivalent to RecordingPointPen except it splits contours from components, so it can't always exactly reproduce the calling sequence of a point pen. So I'm +1 on removing DataPointPen, oping that it's not yet used a lot in the wild.

[justvanrossum]

Btw. the change that @cjchapman mentions is caused by the addition of the identifier argument to beginPath(), which happened before fontPens existed. It seems rather accidental.

On the other hand, without beginPath being output, the "points only" digest is rather ambiguous, because all contour points are just concatenated together, contour info is lost completely.

I have no idea what the designed purpose of getDigestPointsOnly() was, the whole thing looks rather messy.