[BUG]: NPY_HALF is not supported

[jchen351]

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Problem description

NPY_HALF is supported by Numpy but not yet supported by pybind11.

From numpy/ndarraytypes.h there is enum NPY_TYPES { ... NPY_HALF, ...}.
However, from pybind11/numpy.h

struct npy_api {
    enum constants { ... } 

, it doesn't have NPY_HALF_

Reproducible example code

No response

[Skylion007]

There is a workaround here: #1776 Since we don't support any versions of Numpy that don't have np.half anymore, I would welcome a PR that added these additions to the master.

[swillisart]

I'm working on a PR for this and have some questions. See discussion #4627 :)