Add stubs for MeshTagsMetaClass

[jorgensd]

To make it possible to use mypy with external libraries.

Otherwise, one would get errors like:

library/file.py:74: error: "MeshTagsMetaClass" has no attribute "dim"
library/file.py:114: error: "MeshTagsMetaClass" has no attribute "indices"
library/file.py:114: error: "MeshTagsMetaClass" has no attribute "values"

Also add the correct ignores to make sure we catch other API changes.

[jhale]

Perhaps you need to define an explicit setter for name?

[jorgensd]

Perhaps you need to define an explicit setter for name?

To do that I had to rename the C++ property name, otherwise I got a recursion error.. However, then the signature of MeshTagsMetaClass and cpp.MeshTags<T> are different, and dolfinx.mesh.meshtags_from_entities returns a different object than

[garth-wells]

The underscore looks wrong in a demo - it's not idiomatic.

[garth-wells]

This doesn't look good. We should seek a proper solution before merging.

[jorgensd]

You cannot have the same name for a property exposed to Python that has a getter and setter (causes infinite recursion). This would be the natural way to expose variables in a pythonic way. The main problem is that the MeshTagMetaClass is not used for all constructors of meshtags in the Python layer, thus making it very hard to use typing and mypy for external libraries.

[jhale]

One option instead of retyping the entire C++ module in python would be to automatically generate stubs (pyi files) for our pybind11 module:

https://mypy.readthedocs.io/en/stable/stubgen.html

or

https://github.com/sizmailov/pybind11-stubgen

However, I couldn't get it to work, admittedly only a five minute try.

[tiagovla]

stubgen -p cpp in the same location of cpp.so should do it.

[jorgensd]

The main issue is that the directory of cpp.so depends on the installation process (and should preferably be executed when installing the pybind layer in setup.py). I do not think we want users to have to generate stubs manually.

[tiagovla]

Usually those tools produce draft stubs which often require some manual updates, I thought those would be committed. Creating them on-the-fly in setup.py is also possible, but it would introduce dependencies. Additionally, if the package is already installed stubgen -p dolfinx.cpp will find it.

[jhale]

@jorgensd Further to your comment #2219 (comment), do you not think that the 'fix' then would be to use the Pythonic constructors for MeshTags throughout?

[jorgensd]

I think that would be the correct way of fixing it. It would mean that we need to wrap up xdmf.read_meshtags
and meshtags_from_entities. I guess we would need to use the C++ copy constructor to transfer the data from C++ to Python, or do you have any other suggestion as to how we could do this in a nice way?

[jorgensd]

Close this for now. Issue made: #2348