def pbkdf2_bin(data, salt, iterations=DEFAULT_PBKDF2_ITERATIONS,
               keylen=None, hashfunc=None):
    """Returns a binary digest for the PBKDF2 hash algorithm of `data`
    with the given `salt`. It iterates `iterations` times and produces a
    key of `keylen` bytes. By default, SHA-1 is used as hash function;
    a different hashlib `hashfunc` can be provided.

    .. versionadded:: 0.9

    :param data: the data to derive.
    :param salt: the salt for the derivation.
    :param iterations: the number of iterations.
    :param keylen: the length of the resulting key.  If not provided
                   the digest size will be used.
    :param hashfunc: the hash function to use.  This can either be the
                     string name of a known hash function or a function
                     from the hashlib module.  Defaults to sha1.
    """
    if isinstance(hashfunc, string_types):
        hashfunc = _hash_funcs[hashfunc]
    elif not hashfunc:
        hashfunc = hashlib.sha1
    data = to_bytes(data)
    salt = to_bytes(salt)

    # If we're on Python with pbkdf2_hmac we can try to use it for
    # compatible digests.
    if _has_native_pbkdf2:
        _test_hash = hashfunc()
        if hasattr(_test_hash, 'name') and \
                        _test_hash.name in _hash_funcs:
            return hashlib.pbkdf2_hmac(_test_hash.name,
                                       data, salt, iterations,
                                       keylen)

    mac = hmac.HMAC(data, None, hashfunc)
    if not keylen:
        keylen = mac.digest_size

    def _pseudorandom(x, mac=mac):
        h = mac.copy()
        h.update(x)
        return bytearray(h.digest())

    buf = bytearray()
    for block in range_type(1, -(-keylen // mac.digest_size) + 1):
        rv = u = _pseudorandom(salt + _pack_int(block))
        for i in range_type(iterations - 1):
            u = _pseudorandom(bytes(u))
            rv = bytearray(starmap(xor, izip(rv, u)))
        buf.extend(rv)
    return bytes(buf[:keylen])

def get_current_traceback(ignore_system_exceptions=False, show_hidden_frames=False, skip=0):
    """Get the current exception info as `Traceback` object.  Per default
    calling this method will reraise system exceptions such as generator exit,
    system exit or others.  This behavior can be disabled by passing `False`
    to the function as first parameter.
    """
    exc_type, exc_value, tb = sys.exc_info()
    if ignore_system_exceptions and exc_type in system_exceptions:
        raise
    for x in range_type(skip):
        if tb.tb_next is None:
            break
        tb = tb.tb_next
    tb = Traceback(exc_type, exc_value, tb)
    if not show_hidden_frames:
        tb.filter_hidden_frames()
    return tb

def gen_salt(length):
    """Generate a random string of SALT_CHARS with specified ``length``."""
    if length <= 0:
        raise ValueError('Salt length must be positive')
    return ''.join(_sys_rng.choice(SALT_CHARS) for _ in range_type(length))

_signature_cache = WeakKeyDictionary()
_epoch_ord = date(1970, 1, 1).toordinal()
_cookie_params = set((b'expires', b'path', b'comment',
                      b'max-age', b'secure', b'httponly',
                      b'version'))
_legal_cookie_chars = (string.ascii_letters +
                       string.digits +
                       u"!#$%&'*+-.^_`|~:").encode('ascii')

_cookie_quoting_map = {
    b',' : b'\\054',
    b';' : b'\\073',
    b'"' : b'\\"',
    b'\\' : b'\\\\',
}
for _i in chain(range_type(32), range_type(127, 256)):
    _cookie_quoting_map[int_to_byte(_i)] = ('\\%03o' % _i).encode('latin1')


_octal_re = re.compile(b'\\\\[0-3][0-7][0-7]')
_quote_re = re.compile(b'[\\\\].')
_legal_cookie_chars_re = b'[\w\d!#%&\'~_`><@,:/\$\*\+\-\.\^\|\)\(\?\}\{\=]'
_cookie_re = re.compile(b"""(?x)
    (?P<key>[^=]+)
    \s*=\s*
    (?P<val>
        "(?:[^\\\\"]|\\\\.)*" |
         (?:.*?)
    )
    \s*;
""")

def gen_salt(length):
    """Generate a random string of SALT_CHARS with specified ``length``."""
    if length <= 0:
        raise ValueError("requested salt of length <= 0")
    return "".join(_sys_rng.choice(SALT_CHARS) for _ in range_type(length))