import hmac
import hashlib
import struct

is_python2 = True

def pbkdf_two(passwd, salt, iters=2048, keylen=64, digestmod=hashlib.sha512):
    import hmac
    import struct
    import hashlib
    dgsz = digestmod().digest_size if callable(digestmod) else digestmod.digest_size
    pwd, salt = [x if isinstance(x, bytes) else bytes(x, 'utf-8') for x in (passwd, salt)]
    if keylen is None: keylen = dgsz
    # Helper function which copies each iteration for h, where h is an hmac seeded with password
    def pbhelper(h, salt, itercount, blocksize):
        import struct
        def prf(h, data):
            hm = h.copy()
            hm.update(data)
            return hm.digest()
        U = prf(h, salt + struct.pack('>i', blocksize))
        T = U
        for j in range(2, itercount+1):
            U = prf(h, U)
            T = "".join([chr( ord(x) ^ ord(y) ) for (x, y) in zip( T, U )]) \
                  if is_python2 else bytes([x ^ y for (x, y) in zip(T, U)])    # XORing
        return T
    L = int(keylen/dgsz) if (keylen%dgsz) else int(keylen/dgsz)+1    # L - number of output blocks to produce
    #if keylen % dgsz != 0: L += 1
    h = hmac.new(key=passwd, msg=None, digestmod=digestmod )
    T = b""
    for i in range(1, L+1):
        T += pbhelper(h, salt, iters, i)
    return T[:keylen]