#! /usr/bin/env python
import sys
import bencode

torrentIn = sys.argv[1]
tracker = sys.argv[2]
torrentOut = sys.argv[3]

with open(torrentIn, 'rb') as f:
    bencoded = f.read()

data = bencode.bdecode(bencoded)
data['announce'] = tracker
bencoded = bencode.bencode(data)

with open(torrentOut, 'wb') as f:
    f.write(bencoded)