Building Cython code¶
Cython code must, unlike Python, be compiled. This happens in two stages:
.pyxfile is compiled by Cython to a
.cfile, containing the code of a Python extension module
.cfile is compiled by a C compiler to a
.pydon Windows) which can be
import-ed directly into a Python session.
There are several ways to build Cython code:
- Write a distutils
pyximport, importing Cython
.pyxfiles as if they were
.pyfiles (using distutils to compile and build in the background).
- Run the
cythoncommand-line utility manually to produce the
.cfile from the
.pyxfile, then manually compiling the
.cfile into a shared object library or DLL suitable for import from Python. (These manual steps are mostly for debugging and experimentation.)
- Use the [IPython] notebook or the [Sage] notebook, both of which allow Cython code inline.
Currently, distutils is the most common way Cython files are built and distributed. The other methods are described in more detail in the Source Files and Compilation section of the reference manual.
Building a Cython module using distutils¶
Imagine a simple “hello world” script in a file
def say_hello_to(name): print("Hello %s!" % name)
The following could be a corresponding
from distutils.core import setup from Cython.Build import cythonize setup( name = 'Hello world app', ext_modules = cythonize("hello.pyx"), )
To build, run
python setup.py build_ext --inplace. Then simply
start a Python session and do
from hello import say_hello_to and
use the imported function as you see fit.
Using the IPython notebook¶
Cython can be used conveniently and interactively from a web browser through the IPython notebook. To install IPython, e.g. into a virtualenv, use pip:
(venv)$ pip install "ipython[notebook]" (venv)$ ipython notebook
To enable support for Cython compilation, install Cython and load the
Cython extension from within IPython:
Then, prefix a cell with the
%%cython marker to compile it:
%%cython cdef int a = 0 for i in range(10): a += i print a
You can show Cython’s code analysis by passing the
%%cython --annotate ...