There can be only one (enum instance) #1177

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1. televator commented on Jun 4, 2019

   

   televator

   on Jun 4, 2019

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   This is still an issue with 2.2.4 and very error-prune as the python doc explicitly encourages to check enum values for identity.

   Minimal example to reproduce

   #include <pybind11/pybind11.h>
   
   namespace py = pybind11;
   
   PYBIND11_MODULE(example_py, m) {
   
       enum class ScopedEnum {
           Two = 2,
           Three
       };
       m.def("return_two", [](){return ScopedEnum::Two;});
       py::enum_<ScopedEnum>(m, "ScopedEnum")
           .value("Two", ScopedEnum::Two)
           .value("Three", ScopedEnum::Three);
   }
   

   produces this situation

   In [1]: import example_py
   
   In [2]: x = example_py.ScopedEnum.Two
   
   In [3]: y = example_py.ScopedEnum.Two
   
   In [4]: z = example_py.return_two()
   
   In [5]: x is y # BUT...
   Out[5]: True
   
   In [6]: x is z
   Out[6]: False
   
   In [7]: x == z
   Out[7]: True
   
2. Skylion007

   added

   enhancement

   help wanted

   bug

   on Sep 8, 2021
3. lucmans commented on Jul 4, 2023

   

   lucmans

   on Jul 4, 2023

   Last edited by lucmans

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   @rwgk We're still running into this issue on pybind11 2.9.1 with the minimal repro provided by @televator. Any update on this?
4. rwgk commented on Jul 4, 2023

   

   rwgk

   on Jul 4, 2023

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   @rwgk We're still running into this issue on pybind11 2.9.1 with the minimal repro provided by @televator. Any update on this?

   I could be wrong, but I'm operating under the assumption that the py::enum_ behavior is practically unchangeable/unfixable, merely because it's in wide use.

   Therefore I added py::native_enum as an alternative here:

   • https://github.com/google/pywrapcc/blob/1a9ac015439b7cecafffae039d138223a10dd5a1/include/pybind11/native_enum.h

   • https://github.com/google/pywrapcc/blob/1a9ac015439b7cecafffae039d138223a10dd5a1/tests/test_native_enum.py

   Note that that's in another repo, although it's actually more-or-less just another branch.

   Could this be merged into pybind11 master? — In theory yes, easily (git merge will just work), in practice it seems extremely unlikely to me. pybind11 master has been in extremely conservative mode for a very long time.

   You could use the pywrapcc branch and it'll fully interoperate with pybind11 master. There is just no pip-installable release.
5. lucmans commented on Jul 5, 2023

   

   lucmans

   on Jul 5, 2023

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   Thank you for the quick response. It's very unfortunate that it won't likely be merged into master.
   I'll look into the native enum in your repo.

   Since the Python docs seem to prefer comparison by identity, I think the pybind11 docs should put a warning in the related section that it isn't supported.
6. rwgk commented on Jul 5, 2023

   

   rwgk

   on Jul 5, 2023

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   I think the pybind11 docs should put a warning in the related section that it isn't supported.

   Please send a PR. I'll look quickly.
7. lucmans commented on Jul 7, 2023

   

   lucmans

   on Jul 7, 2023

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   Here is the PR.
   #4732