Conversions between Python's native (stdlib) enum types and C++ enums. by rwgk · Pull Request #30005 · google/pybind11clif · GitHub

Description

Alternative to py::enum_, binding C++ enum types to Python's native (stdlib) enum types. For example:

enum class altitude : char {
    high = 'h',
    low = 'l'
};

PYBIND11_MODULE(native_enum_demo, m) {
    m += py::native_enum<altitude>("altitude")
             .value("high", altitude::high)
             .value("low", altitude::low);
}

Note that the py::native_enum design is different from the established py::enum_ design:

    py::enum_<altitude>(m, "altitude")
             .value("high", altitude::high)
             .value("low", altitude::low);

The py::native_enum design is a mostly a trick:

Python's native enums cannot be built incrementally, but all name/values need to be passed at once.
To achieve this, py::native_enum is merely a buffer for collecting the name/value pairs. The m += operation triggers harvesting those from the buffer to build the arguments for constructing a native Python enum type.

Sidesteps issues discovered under pybind/pybind11#2744.

This PR fixes pybind/pybind11#3643 (comment), more-or-less as a side-effect.

This PR was transferred from pybind/pybind11#4349, which in turn was transferred from pybind/pybind11#4329.

Suggested changelog entry:

The patch .rej below are resolved, but THIS STATE DOES NOT BUILD: ``` clang++ -o pybind11/tests/test_constants_and_functions.os -c -std=c++17 -fPIC -fvisibility=hidden -O0 -g -Wall -Wextra -Wconversion -Wcast-qual -Wdeprecated -Wundef -Wnon-virtual-dtor -Wunused-result -Werror -isystem /usr/include/python3.10 -isystem /usr/include/eigen3 -DPYBIND11_STRICT_ASSERTS_CLASS_HOLDER_VS_TYPE_CASTER_MIX -DPYBIND11_ENABLE_TYPE_CASTER_ODR_GUARD_IF_AVAILABLE -DPYBIND11_TEST_BOOST -Ipybind11/include -I/usr/local/google/home/rwgk/forked/pybind11/include -I/usr/local/google/home/rwgk/clone/pybind11/include /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:11: In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/pybind11_tests.h:3: In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/eval.h:14: /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:1781:9: error: static_assert failed due to requirement '!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype' "py::class_ holder vs type_caster mismatch: missing PYBIND11_TYPE_CASTER_BASE_HOLDER(T, ...) or collision with custom py::detail::type_caster<T>?" static_assert(!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype, ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:2460:11: note: in instantiation of function template specialization 'pybind11::class_<MyEnum>::class_<>' requested here : class_<Type>(scope, name, extra...), m_base(*this, scope) { ^ /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:106:5: note: in instantiation of function template specialization 'pybind11::enum_<MyEnum>::enum_<>' requested here py::enum_<MyEnum>(m, "MyEnum") ^ 1 error generated. ``` ________ ``` rwgk.c.googlers.com:~/forked/pybind11 $ patch -p 1 < ~/native_enum_git_diff_master_2022-11-19+131942.patch patching file .github/workflows/python312.yml patching file CMakeLists.txt Hunk google#1 FAILED at 111. Hunk google#2 succeeded at 138 (offset 5 lines). 1 out of 2 hunks FAILED -- saving rejects to file CMakeLists.txt.rej patching file include/pybind11/cast.h Hunk google#1 FAILED at 12. Hunk google#2 succeeded at 78 (offset 30 lines). Hunk google#3 succeeded at 1173 (offset 41 lines). 1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/cast.h.rej patching file include/pybind11/detail/abi_platform_id.h patching file include/pybind11/detail/cross_extension_shared_state.h patching file include/pybind11/detail/internals.h Hunk google#1 FAILED at 16. Hunk google#2 succeeded at 109 (offset 1 line). Hunk google#3 FAILED at 203. Hunk google#4 succeeded at 398 (offset 11 lines). Hunk google#5 succeeded at 457 (offset 11 lines). 2 out of 5 hunks FAILED -- saving rejects to file include/pybind11/detail/internals.h.rej patching file include/pybind11/detail/native_enum_data.h patching file include/pybind11/detail/type_map.h patching file include/pybind11/embed.h patching file include/pybind11/native_enum.h patching file include/pybind11/pybind11.h Hunk google#1 FAILED at 12. Hunk google#2 succeeded at 1269 (offset 1 line). Hunk google#3 succeeded at 2457 (offset 255 lines). 1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/pybind11.h.rej patching file include/pybind11/pytypes.h patching file tests/CMakeLists.txt Hunk google#1 succeeded at 160 (offset 18 lines). patching file tests/conftest.py patching file tests/extra_python_package/test_files.py Hunk google#2 FAILED at 47. 1 out of 2 hunks FAILED -- saving rejects to file tests/extra_python_package/test_files.py.rej patching file tests/test_embed/test_interpreter.cpp patching file tests/test_enum.cpp patching file tests/test_enum.py patching file tests/test_native_enum.cpp patching file tests/test_native_enum.py ```

…ence`

…python_state_dict()`

For completeness: We reviewed this PR together in a meeting, spending a good 40 minutes looking at it.

rwgk added 11 commits November 19, 2022 13:39

Make smart_holder code compatible with type_caster_enum_type

a45bb61

Fix if condition guarding `Unable to cast native enum type to refer…

3ec457a

…ence`

WIP native_enum_add_to_parent

9e940e7

PYBIND11_SILENCE_MSVC_C4127

f344bfa

Merge branch 'smart_holder' into native_enum_sh

41cf4ce

Merge branch 'smart_holder' into native_enum_sh

b5f8cde

Merge branch 'smart_holder' into native_enum_sh

78bfc94

Transfer upstream.yml/python312.yml changes from PR google#4397

10253a1

clang-tidy (clang 15) auto-fix

8690a88

Merge branch 'smart_holder' into native_enum_sh

613b46e

This was referenced Mar 9, 2023

[smart_holder] Conversions between Python's native (stdlib) enum types and C++ enums. pybind/pybind11#4349

Closed

New python312dev.yml (to replace upstream.yml) #30006

Merged

rwgk added 4 commits March 9, 2023 07:09

Remove python312.yml: this is handled separately under PR google#30006

822f988

Merge branch 'google_pywrapcc_main' into native_enum_pywrapcc

5f23bee

Fixes for ruff

38559c3

Merge branch 'google_pywrapcc_main' into native_enum_pywrapcc

630ba5f

rwgk added the gha_wf_python312dev_enable Enable python312dev.yml label Mar 9, 2023

rwgk added 2 commits March 13, 2023 18:24

Replace PyEval_GetBuiltins() in finalize_interpreter() with `get_…

3104a35

…python_state_dict()`

Bug fix: Ensure state_dict is destroyed before Py_Finalize()

498c1d2

rwgk mentioned this pull request Mar 14, 2023

Introduce get_python_state_dict() for Python 3.12 compatibility. #30007

Merged

rwgk added 3 commits March 14, 2023 18:09

Restore tests/test_embed/test_interpreter.cpp from google_pywrapcc_main

4f5a125

Restore include/pybind11/embed.h from google_pywrapcc_main

0a59ad2

Merge branch 'google_pywrapcc_main' into native_enum_pywrapcc_wrk

4312d6e

rwgk mentioned this pull request Mar 15, 2023

Add detail/cross_extension_shared_state.h #30008

Merged

rwgk added 2 commits March 15, 2023 13:49

Undo unrelated one-line change (from auto to internals).

fdfb78a

Merge branch 'google_pywrapcc_main' into native_enum_pywrapcc

8f24fc9

rwgk mentioned this pull request Mar 15, 2023

Fix small oversight in PR #30008 #30009

Merged

rwgk added 2 commits March 15, 2023 15:12

Merge branch 'google_pywrapcc_main' into native_enum_pywrapcc

531992c

Add missing test_class_with_enum

1dde266

Add note to docs/classes.rst pointing to PR google#30005

0a9c6fb

rwgk requested a review from wangxf123456 March 16, 2023 00:16

rwgk marked this pull request as ready for review March 16, 2023 00:16

wangxf123456 approved these changes Mar 16, 2023

View reviewed changes

rwgk merged commit f8128f0 into google:main Mar 16, 2023

github-actions Bot added the needs changelog label Mar 16, 2023

rwgk deleted the native_enum_pywrapcc branch March 16, 2023 19:12

rwgk removed the needs changelog label Nov 2, 2023

rwgk mentioned this pull request Jul 31, 2024

[smart_holder] Conversions between Python's native (stdlib) enum types and C++ enums. pybind/pybind11#5280

Closed

rwgk mentioned this pull request Mar 8, 2025

feat: enable conversions between native Python enum types and C++ enums pybind/pybind11#5555

Merged

Conversions between Python's native (stdlib) enum types and C++ enums. by rwgk · Pull Request #30005 · google/pybind11clif · GitHub

Conversions between Python's native (stdlib) enum types and C++ enums. - #30005

Conversions between Python's native (stdlib) enum types and C++ enums.#30005
rwgk merged 25 commits into
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rwgk:native_enum_pywrapcc

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Conversions between Python's native (stdlib) enum types and C++ enums. by rwgk · Pull Request #30005 · google/pybind11clif · GitHub

Conversions between Python's native (stdlib) enum types and C++ enums. - #30005

Conversions between Python's native (stdlib) enum types and C++ enums.#30005rwgk merged 25 commits intogoogle:maingoogle/pybind11clif:mainfrom rwgk:native_enum_pywrapccrwgk/pybind11clif:native_enum_pywrapccCopy head branch name to clipboard

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Conversions between Python's native (stdlib) enum types and C++ enums.#30005
rwgk merged 25 commits into
google:mainfrom
rwgk:native_enum_pywrapcc

rwgk commented Mar 9, 2023 •
edited
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