Can you cimport an .so file?

问题

I have an .so file called tissue-classifier.cpython-37m-x86_64-linux-gnu.so from an external library that I want to import so that I can extend it in one of my local classes. Since I am extending a class, I need to import it as an extension type using cimport and I am wondering if this is even possible. If I use a normal import statement then I will be left with a Python compiled version which cannot be used to extend a cdef class in my current file.

When I try to cimport the tissue_classifier file, it gives me the error that tissue_classifier.pxd file could not be found which makes sense since it is in .so format. Sorry if this is a dumb question, I just haven't been able to figure this out for a while.

回答1:

No, a *.so-file cannot be cimported.

If one is having C/CPP-backgrounds, then pyx/pxd/so-business is propably easiest to understand using the following model:

• the resulting extension (*.so-file) corresponds to the final artefact in C/CPP-world which could be an executable, a shared-object (*.so), or a library/object-file collection. If you just runs the resulting program it is all you need. For example you can use (and probably do) a CPython-interpreter without having built it or having its source code. In analogy, if you have a binary extension (*.so) you can import and use it whitout having to build it (or even having corresponding pyx-files or a compiler on your machine) - that is what is provided by a wheel.
• *.pyx corresponds to c/cpp-files, which have the definitions of the functionality. These files are needed if you want to build the resulting artifact from the source. In C/CPP-world this build process would be triggered by using make or similar. pyx-files are needed if you install the package via python setup.py install - which corresponds to calling make.
• *.pxd corresponds to headers (h/hpp-files): it decribes the functionality in the resulting so-files, so it can be reused. For example just having CPython-interpreter isn't enough to build extensions - one has to install the dev-version so also the includes Python.h&Co. are present at the machine.

So what can be done?

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First possibility:

If authors of the package consider *.pxd-files being part of the public API, then they can put the corresponding pxd-files next to *.so-files into the installation, so the c-interface of the module can be used/extended.

If they don't put the pxd-file into the installation, so chances are high that this c-interface is an implementation detail and you should not be using it, as it may change without notice in the future.

However, it is possible to take the risk and to copy the necessary pxd-files to the installation per hand, but making first sure that it is the right pxd-version (i.e. the same with which so-files in the installation were built).

Second possibility:

The easiest way to ensure, that the right pxd-version is used is to build package from the source, i.e.

• dowloading the the right versioin from github (master or last release)
• calling python setup.py install or what README tells you to do

Now, instead of copying pdx-files to the installation, one could add include_path to the downloaded package-source via include_path for cythonize-function or by adding it to sys.path.

Alternatively, as @BeforeFlight has pointed out in the comments, one could use python setup.py develop (or pip install -e the same folder so it can be deinstalled), and because it creates a link instead of copying data, the pxd-files will be found.

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The above solutions will help to build the module, distributing it is a completely different story however.

来源：https://stackoverflow.com/questions/56776685/can-you-cimport-an-so-file