Commit b9904c3d authored by Stefan Behnel's avatar Stefan Behnel

extend C interaction docs to show how to cpdef an external C function

--HG--
extra : amend_source : d2906987d10e7770ca09dde406219fb0d6a5d38c
parent 28540988
......@@ -22,14 +22,20 @@ by the ``stdlib.h`` header file. This can be done as follows::
return atoi(s) # note: atoi() has no error detection!
You can find a complete list of these standard cimport files in
Cython's source package ``Cython/Includes/``. It also has a complete
set of declarations for CPython's C-API. For example, to test at C
compilation time which CPython version your code is being compiled
with, you can do this::
Cython's source package
`Cython/Includes/ <https://github.com/cython/cython/tree/master/Cython/Includes>`_.
They are stored in ``.pxd`` files, the standard way to provide reusable
Cython declarations that can be shared across modules
(see :ref:`sharing-declarations`).
Cython also has a complete set of declarations for CPython's C-API.
For example, to test at C compilation time which CPython version
your code is being compiled with, you can do this::
from cpython.version cimport PY_VERSION_HEX
print PY_VERSION_HEX >= 0x030200F0 # Python version >= 3.2 final
# Python version >= 3.2 final ?
print PY_VERSION_HEX >= 0x030200F0
Cython also provides declarations for the C math library::
......@@ -50,18 +56,18 @@ shared library ``m``. For distutils, it is enough to add it to the
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
from Cython.Build import cythonize
ext_modules=[
Extension("demo",
["demo.pyx"],
libraries=["m"]) # Unix-like specific
sources=["demo.pyx"],
libraries=["m"] # Unix-like specific
)
]
setup(
name = "Demos",
cmdclass = {"build_ext": build_ext},
ext_modules = ext_modules
ext_modules = cythonize(ext_modules)
)
......@@ -86,6 +92,26 @@ to declare and call into any C library as long as the module that
Cython generates is properly linked against the shared or static
library.
Note that you can easily export an external C function from your Cython
module by declaring it as ``cpdef``. This generates a Python wrapper
for it and adds it to the module dict. Here is a Cython module that
provides direct access to the C ``sin()`` function for Python code::
"""
>>> sin(0)
0.0
"""
cdef extern from "math.h":
cpdef double sin(double x)
You get the same result when this declaration appears in the ``.pxd``
file that belongs to the Cython module (i.e. that has the same name,
see :ref:`sharing-declarations`).
This allows the C declaration to be reused in other Cython modules,
while still providing an automatically generated Python wrapper in
this specific module.
Naming parameters
-----------------
......
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