Programmable filter not recognising inputs[0]

I am having trouble creating a programmable filter, it appears that Paraview is not recognising inputs[0]. It gives an error message:
‘NoneType’ object has no attribute ‘getItem
This happens even if my filter just says something trivial like a=inputs[0]
I am using version 5.4.1.

Heather, welcome to the ParaView community. That is a mysterious error. When you created the Programmable Filter, did you have an object selected in the pipeline browser? Another thought: are you sure you created a Programmable Filter and not a Programmable Source by chance?

Yes, definitely have an object selected, and I’m definitely creating a Programmable Filter. Its very strange, I’ve not had this trouble previously.

Please provide your programmable filter code if possible. (584 Bytes)

Hmm, nothing jumps out at me. Do you have a small example dataset that should work with this filter that you can share?