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| Limitations | |
| ########### | |
| Design choices | |
| ^^^^^^^^^^^^^^ | |
| pybind11 strives to be a general solution to binding generation, but it also has | |
| certain limitations: | |
| - pybind11 casts away ``const``-ness in function arguments and return values. | |
| This is in line with the Python language, which has no concept of ``const`` | |
| values. This means that some additional care is needed to avoid bugs that | |
| would be caught by the type checker in a traditional C++ program. | |
| - The NumPy interface ``pybind11::array`` greatly simplifies accessing | |
| numerical data from C++ (and vice versa), but it's not a full-blown array | |
| class like ``Eigen::Array`` or ``boost.multi_array``. ``Eigen`` objects are | |
| directly supported, however, with ``pybind11/eigen.h``. | |
| Large but useful features could be implemented in pybind11 but would lead to a | |
| significant increase in complexity. Pybind11 strives to be simple and compact. | |
| Users who require large new features are encouraged to write an extension to | |
| pybind11; see `pybind11_json <https://github.com/pybind/pybind11_json>`_ for an | |
| example. | |
| Known bugs | |
| ^^^^^^^^^^ | |
| These are issues that hopefully will one day be fixed, but currently are | |
| unsolved. If you know how to help with one of these issues, contributions | |
| are welcome! | |
| - Intel 20.2 is currently having an issue with the test suite. | |
| `#2573 <https://github.com/pybind/pybind11/pull/2573>`_ | |
| - Debug mode Python does not support 1-5 tests in the test suite currently. | |
| `#2422 <https://github.com/pybind/pybind11/pull/2422>`_ | |
| - PyPy3 7.3.1 and 7.3.2 have issues with several tests on 32-bit Windows. | |
| Known limitations | |
| ^^^^^^^^^^^^^^^^^ | |
| These are issues that are probably solvable, but have not been fixed yet. A | |
| clean, well written patch would likely be accepted to solve them. | |
| - Type casters are not kept alive recursively. | |
| `#2527 <https://github.com/pybind/pybind11/issues/2527>`_ | |
| One consequence is that containers of ``char *`` are currently not supported. | |
| `#2245 <https://github.com/pybind/pybind11/issues/2245>`_ | |
| - The ``cpptest`` does not run on Windows with Python 3.8 or newer, due to DLL | |
| loader changes. User code that is correctly installed should not be affected. | |
| `#2560 <https://github.com/pybind/pybind11/issue/2560>`_ | |
| Python 3.9.0 warning | |
| ^^^^^^^^^^^^^^^^^^^^ | |
| Combining older versions of pybind11 (< 2.6.0) with Python on exactly 3.9.0 | |
| will trigger undefined behavior that typically manifests as crashes during | |
| interpreter shutdown (but could also destroy your data. **You have been | |
| warned**). | |
| This issue was `fixed in Python <https://github.com/python/cpython/pull/22670>`_. | |
| As a mitigation for this bug, pybind11 2.6.0 or newer includes a workaround | |
| specifically when Python 3.9.0 is detected at runtime, leaking about 50 bytes | |
| of memory when a callback function is garbage collected. For reference, the | |
| pybind11 test suite has about 2,000 such callbacks, but only 49 are garbage | |
| collected before the end-of-process. Wheels (even if built with Python 3.9.0) | |
| will correctly avoid the leak when run in Python 3.9.1, and this does not | |
| affect other 3.X versions. | |