Setting VtArray elements via index in python does not work with [-1] but does work correctly with other negative indices

[nvmkuruc]

Description of Issue

The python bindings for VtArray implements setting by index in terms of setting by slice, incrementing the index by 1 to create the slice. However, for -1, that creates an empty slice and the operation silently fails.

Steps to Reproduce

1. Append the following test case to testVtArray.py

    def test_SetNegativeIndices(self):
        d = Vt.DoubleArray([1.0, 3.0, 5.0])
        d[-1] = 2.0
        d[-2] = 4.0
        self.assertEqual(d, [1.0, 4.0, 2.0])

2. Build
3. ctest -C Release -R testVtArray
   You should see the following error message.

    self.assertEqual(d, [1.0, 4.0, 2.0])
AssertionError: Vt.DoubleArray(3, (1, 4, 5)) != [1.0, 4.0, 2.0]

You can see that the second element from back was correctly set to 4.0 but the last element was not set to 2.0.

System Information (OS, Hardware)

Linux

Package Versions

Python 3.10
TBB 2020.3

Build Flags

--tests --no-imaging

[sunyab]

Filed as internal issue #USD-8088

[FlorianZ]

@nvmkuruc good find! Are you interested in tackling this? We'd consider a contribution, for sure. Otherwise, we can pursue this internally, but it doesn't currently rise to the top of our internal priority list. Thank you!!

[nvmkuruc]

Happy to submit one, but didn't want to start in case there was a strong opinion about the best fix. My instinct is to just special case -1 and convert it to [-1 + size(), size()).

[gitamohr]

I have a fix for this, thanks for reporting, @nvmkuruc !