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 `_ 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 `_ - Debug mode Python does not support 1-5 tests in the test suite currently. `#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 `_ One consequence is that containers of ``char *`` are currently not supported. `#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 `_ 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 `_. 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.