ctypes example . call qsort() with structure object (on python plane)

ctypes.example2.py

from ctypes import cdll
from ctypes import CFUNCTYPE, sizeof, POINTER, c_int
from ctypes import Structure

libc = cdll.LoadLibrary("libc.so.6")
import random

class Point(Structure):
    _fields_ = [("x", c_int), 
                ("y", c_int)]

    def __repr__(self):
        return "(%d, %d)" % (self.x, self.y)

PointArray6 = Point * 6

xs = [random.randint(1, 600) for i in xrange(6)]
ys = [random.randint(1, 600) for i in xrange(6)]
parr = PointArray6(*(Point(x, y) for x, y in zip(xs, ys)))

def cmp_fn(pa, pb):
    a = pa[0]
    b = pb[0]
    base = a.x - b.x
    if base == 0:
        return a.y - b.y
    else:
        return base


qsort = libc.qsort
qsort.resttype = None

class IterateProxy(object):
    def __init__(self, arr):
        self.arr = arr

    def __len__(self):
        return len(self.arr)

    def __iter__(self):
        return iter(self.arr)

    def __repr__(self):
        return "<%r %s>" % (self.__class__, [x for x in self])


print IterateProxy(parr)
qsort(parr, len(parr), sizeof(Point), CFUNCTYPE(c_int, POINTER(Point), POINTER(Point))(cmp_fn))
print IterateProxy(parr)

"""
<<class '__main__.IterateProxy'> [(3, 267), (84, 380), (454, 507), (156, 180), (125, 470), (334, 578)]>
<<class '__main__.IterateProxy'> [(3, 267), (84, 380), (125, 470), (156, 180), (334, 578), (454, 507)]>
"""