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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 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 has been
- `fixed in Python <https://github.com/python/cpython/pull/22670>`_. As a
- mitigation until 3.9.1 is released and commonly used, pybind11 (2.6.0 or newer)
- includes a temporary 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
- built with Python 3.9.0 will correctly avoid the leak when run in Python 3.9.1.
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