2021-03-08 14:54:22 +00:00
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Limitations
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###########
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Design choices
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^^^^^^^^^^^^^^
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pybind11 strives to be a general solution to binding generation, but it also has
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certain limitations:
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- pybind11 casts away ``const``-ness in function arguments and return values.
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This is in line with the Python language, which has no concept of ``const``
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values. This means that some additional care is needed to avoid bugs that
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would be caught by the type checker in a traditional C++ program.
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- The NumPy interface ``pybind11::array`` greatly simplifies accessing
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numerical data from C++ (and vice versa), but it's not a full-blown array
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class like ``Eigen::Array`` or ``boost.multi_array``. ``Eigen`` objects are
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directly supported, however, with ``pybind11/eigen.h``.
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Large but useful features could be implemented in pybind11 but would lead to a
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significant increase in complexity. Pybind11 strives to be simple and compact.
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Users who require large new features are encouraged to write an extension to
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pybind11; see `pybind11_json <https://github.com/pybind/pybind11_json>`_ for an
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example.
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Known bugs
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^^^^^^^^^^
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These are issues that hopefully will one day be fixed, but currently are
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unsolved. If you know how to help with one of these issues, contributions
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are welcome!
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- Intel 20.2 is currently having an issue with the test suite.
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`#2573 <https://github.com/pybind/pybind11/pull/2573>`_
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- Debug mode Python does not support 1-5 tests in the test suite currently.
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`#2422 <https://github.com/pybind/pybind11/pull/2422>`_
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- PyPy3 7.3.1 and 7.3.2 have issues with several tests on 32-bit Windows.
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Known limitations
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^^^^^^^^^^^^^^^^^
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These are issues that are probably solvable, but have not been fixed yet. A
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clean, well written patch would likely be accepted to solve them.
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- Type casters are not kept alive recursively.
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`#2527 <https://github.com/pybind/pybind11/issues/2527>`_
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One consequence is that containers of ``char *`` are currently not supported.
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`#2245 <https://github.com/pybind/pybind11/issues/2245>`_
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- The ``cpptest`` does not run on Windows with Python 3.8 or newer, due to DLL
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loader changes. User code that is correctly installed should not be affected.
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`#2560 <https://github.com/pybind/pybind11/issue/2560>`_
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Python 3.9.0 warning
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^^^^^^^^^^^^^^^^^^^^
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2021-08-30 22:58:05 +00:00
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Combining older versions of pybind11 (< 2.6.0) with Python on exactly 3.9.0
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will trigger undefined behavior that typically manifests as crashes during
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2021-03-08 14:54:22 +00:00
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interpreter shutdown (but could also destroy your data. **You have been
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warned**).
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2021-08-30 22:58:05 +00:00
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This issue was `fixed in Python <https://github.com/python/cpython/pull/22670>`_.
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As a mitigation for this bug, pybind11 2.6.0 or newer includes a workaround
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specifically when Python 3.9.0 is detected at runtime, leaking about 50 bytes
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of memory when a callback function is garbage collected. For reference, the
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pybind11 test suite has about 2,000 such callbacks, but only 49 are garbage
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collected before the end-of-process. Wheels (even if built with Python 3.9.0)
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will correctly avoid the leak when run in Python 3.9.1, and this does not
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affect other 3.X versions.
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