I am trying to integrate a third party library written in C
with my python
application using Cython
. I have all of the python code written for a test. I am having trouble finding an example for setting this up.
I have a pyd/pyx
file I created manually. The third party has given me a header file (*.h)
and a shared library (*.so)
. As far as I can tell, there are no other dependencies. Can someone provide an example of how to set this up using Cython
and disutils
?
Thanks
Sure !
(In the following, I assume that you already know how to deal with cimport
and the interactions between .pxd
and .pyx
. If this is not completely the case, just ask and I will develop that part as well)
The sample (grabbed from a C++ project of mine, but a C project would work pretty much the same) :
1. The Distutils setup file :
Assuming that the extension to be created will be called myext
and the 3rd party shared library is libexternlib.so
(note the lib* prefix, here)...
# setup.py file
import sys
import os
import shutil
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
# clean previous build
for root, dirs, files in os.walk(".", topdown=False):
for name in files:
if (name.startswith("myext") and not(name.endswith(".pyx") or name.endswith(".pxd"))):
os.remove(os.path.join(root, name))
for name in dirs:
if (name == "build"):
shutil.rmtree(name)
# build "myext.so" python extension to be added to "PYTHONPATH" afterwards...
setup(
cmdclass = {'build_ext': build_ext},
ext_modules = [
Extension("myext",
sources=["myext.pyx",
"SomeAdditionalCppClass1.cpp",
"SomeAdditionalCppClass2.cpp"
],
libraries=["externlib"], # refers to "libexternlib.so"
language="c++", # remove this if C and not C++
extra_compile_args=["-fopenmp", "-O3"],
extra_link_args=["-DSOME_DEFINE_OPT",
"-L./some/extra/dependency/dir/"]
)
]
)
Note : Your external .so
file is linked via the libraries
option :
libraries=["externlib"] # Without the 'lib' prefix and the '.so' extension...
Note : the sources
option can be used to get some additional source files compiled.
Important : myext.pxd
(do not confound with .pyd
- Windows stuff) and myext.pyx
should be in the same directory. At compile time the definition file, if it exists, is processed first (more).
2. Then run it as follows :
After having changed directory to the one containing your myext.pxd
, your myext.pyx
, as well as the above setup.py
script :
# setup.sh
# Make the "myext" Python Module ("myext.so")
CC="gcc" \
CXX="g++" \
CFLAGS="-I./some/path/to/includes/ -I../../../DEPENDENCIES/python2.7/inc -I../../../DEPENDENCIES/gsl-1.15" \
LDFLAGS="-L./some/path/to/externlib/" \
python setup.py build_ext --inplace
Where :
libexternlib.so
is assumed to be located at ./some/path/to/externlib/
yourheader.h
is assumed to be located at ./some/path/to/includes/
Note : CFLAGS
could also have been setup using the extra_compile_args
option :
extra_compile_args=["-I./some/path/to/includes/", "-fopenmp", "-O3"]
Note : LDFLAGS
could also have been setup using the extra_link_args
option :
extra_link_args=["-L./some/path/to/externlib/", "-DSOME_DEFINE_OPT", "-L./some/extra/dependency/dir/"]
Once distutils is done with the build, you get some new files, specially the myext.cpp
, myext.h
and most importantly, the myext.so
.
3. After that, you're good to go :
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:./some/path/to/externlib/
export PYTHONPATH=$PYTHONPATH:./some/path/to/myext/
# Run some script requiring "myext.so"
python somescript.py
Where your freshly created Python extension can be imported by its name :
# somescript.py
import myext
from myext import PySomeFeature
...
Note about Optimization : By default -O2
is used for compiling the extension, but this can be overloaded (see above setup where -O3
is specified).
Note about Cython paths : If Cython was installed in a custom directory, you might want to add it to your environment, before all :
PYTHONPATH=$PYTHONPATH:../../../DEPENDENCIES/Cython-0.18 export PYTHONPATH;
PATH=$PATH:../../../DEPENDENCIES/Cython-0.18/bin; export PATH;
Well, hope I covered the main points...