Pyximport.install() can break the build of projects using pypng

[adefazio]

I had the problem that after importing pypng into my project, none of my cython code worked anymore. It was caused by pyximport, which is setup in png.py. When pyximport.install() is called, it takes over compilation of cython code for the whole process, not just the file it was called in. So instead of my cython code being compiled using the correct flags that I specified in setup.py, it was being compiled using the default parameters by pyximport, which broke things.

[drj11]

I don't use Cython, but that sounds pretty horrible.

Do you know how to workaround it?

[drj11]

Sounds like we should do the compilation at installation time, under the control of setup.py. http://docs.cython.org/src/userguide/source_files_and_compilation.html suggests that using Cython.Build.cythonize, will do the trick.

Does a Cython user want to try it out and submit a pull request?

(Have to say, it's NOT GOOD that Cython compilation is affected by flags; by contrast Python compilation is not (or almost is not))

[drj11]

Clearly no library should be doing pyximport.install(). I've removed it from png.py.

Now it's up to a Cython user to correctly compile and install cpngfilters.pyx. I would accept a pull-request that did that compilation step in setup.py.

[Scondo]

I suppose it's better to make '.c' file with Cython, keep it and later compile with extra distutils.extension http://docs.python.org/2/distutils/apiref.html#module-distutils.extension
This provide fast '.c' extension to users without Cython and keep all Cython thing to people who understand them.

I've done this in my fork (but for different reasons).
Also seen this here: e98cuenc/pypng@3c458fc

[drj11]

I will not be distributing a .c file compiled from a .pyx file. Anyone wanting to use pypng compiled by Cython will have to have Cython at installation time.