Image.point(lut, mode) no longer accepts numpy.arrays

[michel4j]

In PIL 1.1.7, you could pass a numpy.array as a look-up-table. However the current version 2.2.1 breaks that behavior by allowing only collections.Sequence instances, which a numpy.array is not.

[aclark4life]

@minkwe Can you trace this regression back in the commit history (assuming numpy.array should still be supported)?

[michel4j]

@aclark4life You can find the change at the bottom of da1d715

Essentially operator.isSequenceType was replaced with collections.Sequence probably to support Python 3 which does not have operator.isSequenceType. But I discovered this because it broke my code when I moved from Pillow 1.7.8 to Pillow 2+:

operator.isSequenceType(numpy.array([1]) # True
isinstance(numpy.array([1]), collections.Sequence) # False for both python 2.7 and 3

There is an outstanding bug request to make numpy a collections.Sequence numpy/numpy#2776. However it would be nice if Pillow continues to support numpy.ndarrays until this is fixed or in the alternative the release notes of Pillow should contain a backward incompatibility warning.

[aclark4life]

OK so Python 3 compat broke numpy.array support, thanks. Is there an operator.isSequenceType equivalent in Python 3, anyone know?

[wiredfool]

Looks like this is the only place in the code where we're likely to get a numpy.array that's going to trigger this bug. (the other mention is in the resolution tag in tiffs, and I just don't see that being a problem).

I'd propose adding an isSequenceType function into the _util.py file that would specifically check for numpy.arrays.

[aclark4life]

+1

[wiredfool]

Also, we need test coverage on this. And the 16bit lut issue as well.

[michel4j]

What about checking if lut is callable and then assuming it is a sequence. Currently the code checks for sequence first and then assumes it is a function. hasattr(lut,"__call__") will work in both Python 2 and Python 3. This avoids adding numpy specifics.

[wiredfool]

@minkwe that would work too. though, as callable(lut). or not. We use isinstance(foo, collections.callable) too. I think they all wind up essentially checking hasattr anyway.