f2py and numpy

Date:2006-08-14 (last modified), 2006-02-18 (created)

Wrapping C codes using f2py

While initially f2py was developed for wrapping Fortran codes for Python, it can be easily used for wrapping C codes as well. Signature files describing the interface to wrapped functions must be created manually and the functions and their arguments must have the attribute . See f2py UsersGuide for more information about the syntax of signature files.

Here follows as simple C code

/* File foo.c */
void foo(int n, double *x, double *y) {
  int i;
  for (i=0;i<n;i++) {
    y[i] = x[i] + i;

and the corresponding signature file

! File m.pyf
python module m
  subroutine foo(n,x,y)
    intent(c) foo                 ! foo is a C function
    intent(c)                     ! all foo arguments are
                                  ! considered as C based
    integer intent(hide), depend(x) :: n=len(x)  ! n is the length
                                                 ! of input array x
    double precision intent(in) :: x(n)          ! x is input array
                                                 ! (or  arbitrary sequence)
    double precision intent(out) :: y(n)         ! y is output array,
                                                 ! see code in foo.c
  end subroutine foo
end interface
end python module m

To build the wrapper, one can either create a setup.py script

In [ ]:
# File setup.py
def configuration(parent_package='',top_path=None):
    from numpy.distutils.misc_util import Configuration
    config = Configuration('',parent_package,top_path)

                         sources = ['m.pyf','foo.c'])
    return config
if __name__ == "__main__":
    from numpy.distutils.core import setup

and execute:

python setup.py build_src build_ext --inplace

Or one can call f2py directly in command line to build the wrapper as follows:

f2py m.pyf foo.c -c

In both cases an extension module will be created to current directory that can be imported to python:

>>> import m
>>> print m.__doc__
This module 'm' is auto-generated with f2py (version:2_2130).
  y = foo(x)
>>> print m.foo.__doc__
foo - Function signature:
  y = foo(x)
Required arguments:
  x : input rank-1 array('d') with bounds (n)
Return objects:
  y : rank-1 array('d') with bounds (n)

>>> print m.foo([1,2,3,4,5])
[ 1.  3.  5.  7.  9.]

Section author: PearuPeterson, AndrewStraw, AlbertStrasheim