python pre-receive for check same blob object

pre-receive.py

#!/usr/bin/python
import sys
import subprocess

data = sys.stdin.read()
_, new_obj, _ = data.split()


def command_output(command):
    output = subprocess.check_output(
        command, shell=True).split("\n")
    result = [l.strip() for l in output if l]
    return result


# get all blob-objects in new_obj
cmd = "git ls-tree -r %s" % new_obj
new_blobs = command_output(cmd)
new_shas = [b.split(" ")[2].split("\t")[0] for b in new_blobs]

# check if have same blob objects
if len(set(new_shas)) < len(new_shas):
    print "reject"
    sys.exit(1)

print "accept"
sys.exit(0)