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 intent(c). 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
interface
  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

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

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

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 m.so 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).
Functions:
  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.]
>>>

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