XXTEA for Python

############################################################   
#                                                          #   
# The implementation of PHPRPC Protocol 3.0                #   
#                                                          #   
# xxtea.py                                                 #   
#                                                          #   
# Release 3.0.0                                            #   
# Copyright (c) 2005-2008 by Team-PHPRPC                   #   
#                                                          #   
# WebSite:  http://www.phprpc.org/                         #   
#           http://www.phprpc.net/                         #   
#           http://www.phprpc.com/                         #   
#           http://sourceforge.net/projects/php-rpc/       #   
#                                                          #   
# Authors:  Ma Bingyao <[email protected]>                  #   
#                                                          #   
# This file may be distributed and/or modified under the   #   
# terms of the GNU Lesser General Public License (LGPL)    #   
# version 3.0 as published by the Free Software Foundation #   
# and appearing in the included file LICENSE.              #   
#                                                          #   
############################################################   
#   
# XXTEA encryption arithmetic library.   
#   
# Copyright (C) 2005-2008 Ma Bingyao <[email protected]>   
# Version: 1.0   
# LastModified: Oct 5, 2008   
# This library is free.  You can redistribute it and/or modify it.   
   
import struct   
   
_DELTA = 0x9E3779B9   
   
def _long2str(v, w):   
    n = (len(v) - 1) << 2   
    if w:   
        m = v[-1]   
        if (m < n - 3) or (m > n): return ''   
        n = m   
    s = struct.pack('<%iL' % len(v), *v)   
    return s[0:n] if w else s   
   
def _str2long(s, w):   
    n = len(s)   
    m = (4 - (n & 3) & 3) + n   
    s = s.ljust(m, "\0")   
    v = list(struct.unpack('<%iL' % (m >> 2), s))   
    if w: v.append(n)   
    return v   
   
def encrypt(str, key):   
    if str == '': return str   
    v = _str2long(str, True)   
    k = _str2long(key.ljust(16, "\0"), False)   
    n = len(v) - 1   
    z = v[n]   
    y = v[0]   
    sum = 0   
    q = 6 + 52 // (n + 1)   
    while q > 0:   
        sum = (sum + _DELTA) & 0xffffffff   
        e = sum >> 2 & 3   
        for p in xrange(n):   
            y = v[p + 1]   
            v[p] = (v[p] + ((z >> 5 ^ y << 2) + (y >> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z))) & 0xffffffff   
            z = v[p]   
        y = v[0]   
        v[n] = (v[n] + ((z >> 5 ^ y << 2) + (y >> 3 ^ z << 4) ^ (sum ^ y) + (k[n & 3 ^ e] ^ z))) & 0xffffffff   
        z = v[n]   
        q -= 1   
    return _long2str(v, False)   
   
def decrypt(str, key):   
    if str == '': return str   
    v = _str2long(str, False)   
    k = _str2long(key.ljust(16, "\0"), False)   
    n = len(v) - 1   
    z = v[n]   
    y = v[0]   
    q = 6 + 52 // (n + 1)   
    sum = (q * _DELTA) & 0xffffffff   
    while (sum != 0):   
        e = sum >> 2 & 3   
        for p in xrange(n, 0, -1):   
            z = v[p - 1]   
            v[p] = (v[p] - ((z >> 5 ^ y << 2) + (y >> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z))) & 0xffffffff   
            y = v[p]   
        z = v[n]   
        v[0] = (v[0] - ((z >> 5 ^ y << 2) + (y >> 3 ^ z << 4) ^ (sum ^ y) + (k[0 & 3 ^ e] ^ z))) & 0xffffffff   
        y = v[0]   
        sum = (sum - _DELTA) & 0xffffffff   
    return _long2str(v, True)   
   
if __name__ == "__main__":   
    print decrypt(encrypt('Hello XXTEA!', '16bytelongstring'), '16bytelongstring')