torrent.py

#decode torrent file
import os
import sys


def decode(f):
    c = f.read(1)
    if c.isdigit(): #string
        len = dec_size(f,c)
        return f.read(len)
    if c == 'd':
        return dec_dict(f)
    if c == 'i':
        return dec_int(f)
    if c == 'l':
        return dec_list(f)
    if c == 'e':
        return None
    return None 
    
def dec_size(f,init=''):
    c = f.read(1)
    num = init
    while c.isdigit():
        num = num + c
        c = f.read(1)
    assert( c == ':' )
    return int(num)
    
def dec_int(f,init=''):
    c = f.read(1)
    num = init
    while c.isdigit():
        num = num + c
        c = f.read(1)
    assert( c == 'e' )
    return int(num)
    
def dec_dict(f):
    ret = {}
    key = decode(f)
    while key:
        value = decode(f)
        ret[key] = value        
        key = decode(f)        
    return ret
    
def dec_list(f):
    ret = []
    item = decode(f)
    while item:        
        ret.append(item)
        item = decode(f)
    return ret
    
def decode_torrent(filename):
    with open(filename,"rb") as f:
        return decode(f)

if __name__ == '__main__':        
    item = decode_torrent(sys.argv[1])
    print item['info']['length']
    print item['info']['name']    
    for k,v in item['info'].iteritems():
        print k