Define length on Annotation Elements

[philippjfr]

Defining a length is part of the core API and I have run into failures which I cannot reproduce right now because the annotations do not support it. Setting length 1 is consistent with how their dimension_values methods work, which return length 1 arrays.

Edit: I threw a bug fix for a small bug on the Arrow Annotation

[jlstevens]

A length of 1 seems reasonable. If __len__ is now required, why not raise a NotImplementedError in the appropriate base class (maybe Element?)

[philippjfr]

I just added a general __len__ implementation for Element which is based on the length of dimension_values along the first dimension. This should work fine because dimension_values HAS to be implemented and the length of the element is always defined as the length of its dimension_values. Subclasses can override for more efficient implementations.

[jlstevens]

Happy to merge once the tests pass.

[philippjfr]

Hmm, so this is problematic, turns out something is actively looking for the __len__ attribute and enabling checks in that case. Since Element doesn't actually have any values but is used all over the tests this now fails. Making it NotImplemented would also fail, really not sure what the best solution is.

[jlstevens]

Hmm, so this is problematic, turns out something is actively looking for the len attribute

My initial reaction is this could be due to testing of the boolean value of elements or pretty printing...

[philippjfr]

@jlstevens I think this is the correct fix now, I'll still try to reproduce the original bug so I can add a unit test.

[philippjfr]

I also just found out that cloning of Text and Arrow types was broken, so any deep selection, redim, relabel etc. was breaking. I've now addressed this by reordering the .data of these types to match the signature and implementing .clone to handle that.

[jlstevens]

Other than one transient error, tests are passing. Ready to merge?

[philippjfr]

Yes, I think it's ready now.

[jlstevens]

Tests have all passed now. Merging.