find holes in sparse files

import os


def find_holes(file):
    with open(file, "rb") as fd:
        fileno = fd.fileno()
        size = os.stat(fileno).st_size
        pos = 0
        holes = []

        while True:
            hole_start = os.lseek(fileno, pos, os.SEEK_HOLE)
            data_start = os.lseek(fileno, pos, os.SEEK_DATA)

            if hole_start == size:
                break

            holes.append((hole_start, data_start))

            if pos == data_start:
                break

            pos = data_start

        return holes