libboost_python3.so.1.56.0: undefined symbol: PyClass_Type

Question

I\'m trying to create a helloWorld module for Python3 in C++ using boost::python library.

Here is a CmakeList.txt:

set(Python_ADDITIONAL         


        

Answer 1

As noted in this answer:

PyClass_Type is is part of the Python 2 C API and not part of the Python 3 C API. Hence, the Boost.Python library was likely built against Python 2. However, it is being loaded by a Python 3 interpreter, where the PyClass_Type is not available.

The exact procedure used to produce libboost_python3.so is not presented, so I can only speculate a non clean build, such as building Boost.Python with Python2, then reconfiguring bootstrap with Python3, and then building Boost.Python with the Python2 object files. Regardless, verify a clean build of Boost.Python with Python3.

$ ./bootstrap.sh --with-python=/usr/bin/python2
...
Detecting Python version... 2.7
$ ./b2 --with-python --buildid=2 # produces libboost_python-2.so
$ ./bootstrap.sh --with-python=/usr/bin/python3 --with-python-root=/usr
...
Detecting Python version... 3.3
$ ./b2 --with-python --buildid=3noclean # produces libboost_python-3noclean.so
$ ./b2 --with-python --clean
$ ./b2 --with-python --buildid=3 # produces libboost_python-3.so

$ nm -D stage/lib/libboost_python-2.so | grep PyClass_Type
                 U PyClass_Type
$ nm -D stage/lib/libboost_python-3noclean.so | grep PyClass_Type
                 U PyClass_Type
$ nm -D stage/lib/libboost_python-3.so | grep PyClass_Type

As expected, libboost_python-2.so references the PyClass_Type symbol. Additionally, the libboost_python-3noclean.so contains a reference to PyClass_Type as it was built with libboost_python-2.so's object files. With a clean build, libboost_python-3.so should not contain a reference to PyClass_Type.