Creates the index file from open record file

def create_index(self):
        """Creates the index file from open record file
        """
        self.reset()
        counter = 0
        pre_time = time.time()
        while True:
            if counter % 1000 == 0:
                cur_time = time.time()
                print('time:', cur_time - pre_time, ' count:', counter)
            pos = self.tell()
            cont = self.read()
            if cont is None:
                break
            key = self.key_type(counter)
            self.fidx.write('%s\t%d\n'%(str(key), pos))
            counter = counter + 1