Using C codes in Python | Set 2 (original) (raw)

Last Updated : 18 Mar, 2019

Prerequisite: Using C codes in Python | Set 1

In the previous article, we have discussed how to access C code in Python. Now, let’s see how to access C functions.

Code #1 : Accessing C functions with Python

import work

print ( "GCD : " , work.gcd( 35 , 42 ))

print ( "\ndivide : " , work.divide( 42 , 8 ))

print ( "\navg : " , work.avg([ 1 , 2 , 3 ]))

p1 = work.Point( 1 , 2 )

p2 = work.Point( 4 , 5 )

print ( "\ndistance : " , work.distance(p1, p2))

Output :

GCD : 7

divide : (5, 2)

avg : 2.0

distance : 4.242640687119285

Issue ?
Now the work done above has an issue that for the overall packaging of C and Python code together, using ctypes to access C code that has been compiled, one has to make sure that the shared library gets placed in a location, where the work.py module can find it. One possibility is to put the resulting libsample.so file in the same directory as the supporting Python code.

So, if the C library is installed elsewhere, then path has to be adjusted accordingly. If it is installed as a standard library on the machine, then ctypes.util.find_library() function can be used.

Code #2 : Path Example

from ctypes.util import find_library

find_library( 'm' )

find_library( 'pthread' )

find_library( 'sample' )

Output :

/usr/lib/libm.dylib

/usr/lib/libpthread.dylib

/usr/local/lib/libsample.so

Again, ctypes won’t work at all if it can’t locate the library with the C code. ctypes.cdll.LoadLibrary() is used to load the C library, once it’s location is known.

_mod = ctypes.cdll.LoadLibrary(_path)