Specify cython output file

Question

It seems that by default setup from distutils.core with cmdclass set to build_ext, compiles a cpp or c file in the current working directory. Is there a way to determine where the generated c code is written to? Otherwise, a repository will be littered with generated code.

For example this file setup.py will write a file example.c to the current working directory:

from distutils.core import setup
from Cython.Build import cythonize

setup(
      ext_modules = cythonize("example.pyx"))

DavidW · Accepted Answer · 2017-05-21T07:43:06.863

22

You can pass the option build_dir="directory name" to Cythonize

# rest of file as before
setup(
      ext_modules = cythonize("example.pyx",
                              build_dir="build"))

The above code will put the generated c files in the directory "build" (which makes sense, since by default it's where distutils puts temporary object files and so forth when it's building).

My original answer had working, not build_dir. Thanks to @ArthurTacca for pointing out that that no longer seems to be right.

edited May 21 '17 at 07:43

answered Dec 22 '15 at 08:27

DavidW

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The correct option seems to be "build_dir" not "working". Perhaps it changed in a recent version of Cython. To avoid clashing with other build files, it's probably best not to just use "build". A subdirectory like "build/cython" would be better. – Arthur Tacca Mar 31 '17 at 14:57
At a quick glance you look to be right - thanks. Looking at the code on github I can't see where it's changed since 2015 so who knows where I got it from (but I imagine it must have worked at the time...). I'll update it once I've confirmed that it does work. – DavidW Mar 31 '17 at 15:27
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But how to specify a path to build the .so files? – Sayan Sen Jun 02 '20 at 06:20

score 14 · Answer 2 · edited Mar 14 '22 at 20:40

14

After initializing an Extension, the parameters can be set to create c in temp directory.

module  = Extension("temp", "temp.pyx")
module.cython_c_in_temp = True

edited Mar 14 '22 at 20:40

Josh Correia

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answered Dec 22 '15 at 20:53

Michael WS

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I think this is a slightly better solution than my answer. – DavidW Jan 01 '16 at 11:39
This solution solved my problem as well but is adding attributes to an `Extension` documented anywhere? – Mathias Laurin Mar 13 '18 at 20:21
No, but we do stuff like that all the time in cython. When I get a chance, we should document all the options – Michael WS Mar 14 '18 at 21:29

score 9 · Answer 3 · answered Jun 23 '16 at 10:31

Your setup.py is fine.

To get it to build to a different location, invoke python in the following way:

python setup.py build_ext --build-lib <build directory>

I use the following make rules to automate this:

python_lib_dir=src/lib

cython_output = $(patsubst $(python_lib_dir)/%.pyx,$(python_lib_dir)/%.so, $(shell find $(python_lib_dir) -name '*.pyx'))

$(cython_output):%.so:%.pyx      
    python setup.py build_ext --build-lib $(python_lib_dir)

Specify cython output file

3 Answers3

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