Is this Boost::Python (Python 3.7) error “__init__() should return None, not 'NoneType'” a linking problem?

Question

Update

I\'m not going to add this as an answer, since I still haven\'t technically solved the problem. But since I\'ve now spent 2.5 days trying to get things to w

Answer 1

Adding an answer here for those using the Anaconda or Conda-Forge Distribution:

The python interpreter statically links in the libpythonXY library. Which is why it makes the python binary different compared to other distributions.

The fix for the problem reported by OP is to use:

-undefined dynamic_lookup

Instead of:

-lpythonXY

You are creating a Python C/C++ extension, and not embedding the python interpreter. So you shouldn't be linking to the python library. Pybind11 handles this correctly.

See the following for more information:

• https://gitlab.kitware.com/cmake/cmake/issues/18100
• https://github.com/ContinuumIO/anaconda-issues/issues/9078

One a side note, python 3.8 has added an additional flag: --embed and only then it adds -lpythonXY in the output:

$ python3.8-config --libs
-ldl -framework CoreFoundation

$ python3.8-config --libs --embed
-lpython3.8 -ldl -framework CoreFoundation