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feat(numpy): add NPY_HALF_ to npy_api::constants #6151

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feat(numpy): add NPY_HALF_ to npy_api::constants #6151

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b34e4c8
feat(numpy): add NPY_HALF_ to npy_api::constants
advitrocks9 Aug 23, 2026
568bd1d
tests: round-trip a user-defined half dtype as numpy.float16
advitrocks9 Aug 23, 2026
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1 change: 1 addition & 0 deletions include/pybind11/numpy.h
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Original file line number Diff line number Diff line change
Expand Up @@ -235,6 +235,7 @@ struct npy_api {
NPY_STRING_,
NPY_UNICODE_,
NPY_VOID_,
NPY_HALF_ = 23, // NPY_DATETIME (21) and NPY_TIMEDELTA (22) are not mirrored
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// Platform-dependent normalization
NPY_INT8_ = NPY_BYTE_,
NPY_UINT8_ = NPY_UBYTE_,
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19 changes: 19 additions & 0 deletions tests/test_numpy_dtypes.cpp
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Expand Up @@ -318,6 +318,21 @@ py::array_t<T> dispatch_array_increment(const py::array_t<T> &arr) {
struct A {};
struct B {};

struct UserHalf {
uint16_t bits;
};

PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
PYBIND11_NAMESPACE_BEGIN(detail)
template <>
struct npy_format_descriptor<UserHalf> {
static constexpr auto name = const_name("numpy.float16");
static constexpr int value = npy_api::NPY_HALF_;
static pybind11::dtype dtype() { return pybind11::dtype(/*typenum*/ value); }
};
PYBIND11_NAMESPACE_END(detail)
PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

TEST_SUBMODULE(numpy_dtypes, m) {
try {
py::module_::import("numpy");
Expand Down Expand Up @@ -646,6 +661,10 @@ TEST_SUBMODULE(numpy_dtypes, m) {
PYBIND11_NUMPY_DTYPE(TrailingPaddingStruct, a, b);
m.def("trailing_padding_dtype", []() { return py::dtype::of<TrailingPaddingStruct>(); });

// test_half_dtype (issue #4061)
m.def("half_dtype_num", []() { return py::dtype::num_of<UserHalf>(); });
m.def("half_roundtrip", [](const py::array_t<UserHalf> &arr) { return arr; });

// test_string_array
m.def("create_string_array", [](bool non_empty) {
py::array_t<StringStruct, 0> arr = mkarray_via_buffer<StringStruct>(non_empty ? 4 : 0);
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7 changes: 7 additions & 0 deletions tests/test_numpy_dtypes.py
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Expand Up @@ -205,6 +205,13 @@ def test_dtype(simple_dtype):
assert (m.test_dtype_switch(arr.astype("longdouble")) == arr + 1).all()


def test_half_dtype():
assert m.half_dtype_num() == np.dtype("float16").num

result = m.half_roundtrip(np.array([1.5, 2.25, -3.0], dtype=np.float16))
assert result.dtype == np.float16


def test_templated_dtype():
"""A type spelled with a comma needs PYBIND11_TYPE here."""
plain, renamed = m.templated_dtypes()
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