How do i read that binary file

reading.py

from struct import unpack

fname = r'D:\vk_1015\group_data_inv.bin'
buffer_size = 1024
last_node = 1
user_subs = {1: []}
stop = False
with open(fname, 'rb') as f:
    while True:
        bytes = f.read(4*buffer_size)
        if len(bytes) == 0:
            break
        buffer_values = unpack('i'*(len(bytes)/4), bytes)
        #print buffer_values
        #break
        for idx, value in enumerate(buffer_values):
            if value <= 0:
                last_node = -value
                if last_node > max(user_subs.keys()):
                    stop = True
                    break
            else:
                if last_node in user_subs:
                    user_subs[last_node].append(value)
        if stop:
            break
        del(bytes)