Python struct.pack() Examples

def _hello_pack(self):
        data = ( self.user.ljust(20,   '\x00'),
                 self.host.ljust(32,   '\x00'),
                 self.vendor.ljust(10, '\x00'),
                 self.tty.ljust(32,    '\x00'),
                 '\x84'.ljust(12,      '\x00'), # ???
                 self.pid.ljust(10,    '\x00'),
                 self.arch.ljust(12,   '\x00') )

        ver = struct.pack("BB", *self.version)
        num = '78\x0014\x00' # ???
        req = ''.join([d+'\x00' for d in data]) + ver + num

        cb = sum(map(ord, req[:len(req)-2]))%256
        prefix = struct.pack('4B', 0x68, # ???
                                   cb,
                                   0x31, # ???
                                   0x33) # ???
        req = prefix + req
        return req

    # TODO many of these response types only occur for certain requests.
    # Refactor this to separate them and move things to the other classes where
    # needed. 

def _header_create(self, data, reqtype=TYPE_REQ):
        # The length of the entire request in bytes, for TYPE_REQ, will be:
        # --- 20 byte prefix + header
        # 4 for the prefix (0x2f + checkbyte + crc)
        # 8 for the header (req len + req type + timestamp)
        # 8 null-padding
        # --- Message
        # 2 for \x01\x04 (what's this?)
        # a varying-length segment with the main data
        # ---
        timestamp = calendar.timegm(time.gmtime()) # Current unix time in UTC
        reqlen = len(data)+HEADERLEN
        # The 18 bytes before prefix, checksum, CRC
        header = struct.pack("!HHL",
                reqlen,
                reqtype,
                timestamp)
        header = header.ljust(16, '\x00')

        return chr(0x2f) + self._checkbytes(header+data) + header 

def _write_header(self, initlength):
        assert not self._headerwritten
        self._file.write('RIFF')
        if not self._nframes:
            self._nframes = initlength / (self._nchannels * self._sampwidth)
        self._datalength = self._nframes * self._nchannels * self._sampwidth
        self._form_length_pos = self._file.tell()
        self._file.write(struct.pack('<L4s4sLHHLLHH4s',
            36 + self._datalength, 'WAVE', 'fmt ', 16,
            WAVE_FORMAT_PCM, self._nchannels, self._framerate,
            self._nchannels * self._framerate * self._sampwidth,
            self._nchannels * self._sampwidth,
            self._sampwidth * 8, 'data'))
        self._data_length_pos = self._file.tell()
        self._file.write(struct.pack('<L', self._datalength))
        self._headerwritten = True 

def test_endian_float(self):
        if sys.byteorder == "little":
            self.assertIs(c_float.__ctype_le__, c_float)
            self.assertIs(c_float.__ctype_be__.__ctype_le__, c_float)
        else:
            self.assertIs(c_float.__ctype_be__, c_float)
            self.assertIs(c_float.__ctype_le__.__ctype_be__, c_float)
        s = c_float(math.pi)
        self.assertEqual(bin(struct.pack("f", math.pi)), bin(s))
        # Hm, what's the precision of a float compared to a double?
        self.assertAlmostEqual(s.value, math.pi, 6)
        s = c_float.__ctype_le__(math.pi)
        self.assertAlmostEqual(s.value, math.pi, 6)
        self.assertEqual(bin(struct.pack("<f", math.pi)), bin(s))
        s = c_float.__ctype_be__(math.pi)
        self.assertAlmostEqual(s.value, math.pi, 6)
        self.assertEqual(bin(struct.pack(">f", math.pi)), bin(s)) 

def test_endian_double(self):
        if sys.byteorder == "little":
            self.assertIs(c_double.__ctype_le__, c_double)
            self.assertIs(c_double.__ctype_be__.__ctype_le__, c_double)
        else:
            self.assertIs(c_double.__ctype_be__, c_double)
            self.assertIs(c_double.__ctype_le__.__ctype_be__, c_double)
        s = c_double(math.pi)
        self.assertEqual(s.value, math.pi)
        self.assertEqual(bin(struct.pack("d", math.pi)), bin(s))
        s = c_double.__ctype_le__(math.pi)
        self.assertEqual(s.value, math.pi)
        self.assertEqual(bin(struct.pack("<d", math.pi)), bin(s))
        s = c_double.__ctype_be__(math.pi)
        self.assertEqual(s.value, math.pi)
        self.assertEqual(bin(struct.pack(">d", math.pi)), bin(s)) 

def test_struct_fields_2(self):
        # standard packing in struct uses no alignment.
        # So, we have to align using pad bytes.
        #
        # Unaligned accesses will crash Python (on those platforms that
        # don't allow it, like sparc solaris).
        if sys.byteorder == "little":
            base = BigEndianStructure
            fmt = ">bxhid"
        else:
            base = LittleEndianStructure
            fmt = "<bxhid"

        class S(base):
            _fields_ = [("b", c_byte),
                        ("h", c_short),
                        ("i", c_int),
                        ("d", c_double)]

        s1 = S(0x12, 0x1234, 0x12345678, 3.14)
        s2 = struct.pack(fmt, 0x12, 0x1234, 0x12345678, 3.14)
        self.assertEqual(bin(s1), bin(s2)) 

def __new_rowid(self, table, txn) :
        """Create a new unique row identifier"""
        unique = 0
        while not unique:
            # Generate a random 64-bit row ID string
            # (note: might have <64 bits of true randomness
            # but it's plenty for our database id needs!)
            blist = []
            for x in xrange(_rowid_str_len):
                blist.append(random.randint(0,255))
            newid = struct.pack('B'*_rowid_str_len, *blist)

            if sys.version_info[0] >= 3 :
                newid = newid.decode("iso8859-1")  # 8 bits

            # Guarantee uniqueness by adding this key to the database
            try:
                self.db.put(_rowid_key(table, newid), None, txn=txn,
                            flags=db.DB_NOOVERWRITE)
            except db.DBKeyExistError:
                pass
            else:
                unique = 1

        return newid 

def save_int(self, obj, pack=struct.pack):
        if self.bin:
            # If the int is small enough to fit in a signed 4-byte 2's-comp
            # format, we can store it more efficiently than the general
            # case.
            # First one- and two-byte unsigned ints:
            if obj >= 0:
                if obj <= 0xff:
                    self.write(BININT1 + chr(obj))
                    return
                if obj <= 0xffff:
                    self.write("%c%c%c" % (BININT2, obj&0xff, obj>>8))
                    return
            # Next check for 4-byte signed ints:
            high_bits = obj >> 31  # note that Python shift sign-extends
            if high_bits == 0 or high_bits == -1:
                # All high bits are copies of bit 2**31, so the value
                # fits in a 4-byte signed int.
                self.write(BININT + pack("<i", obj))
                return
        # Text pickle, or int too big to fit in signed 4-byte format.
        self.write(INT + repr(obj) + '\n') 

def save_string(self, obj, pack=struct.pack):
            unicode = obj.isunicode()

            if self.bin:
                if unicode:
                    obj = obj.encode("utf-8")
                l = len(obj)
                if l < 256 and not unicode:
                    self.write(SHORT_BINSTRING + chr(l) + obj)
                else:
                    s = pack("<i", l)
                    if unicode:
                        self.write(BINUNICODE + s + obj)
                    else:
                        self.write(BINSTRING + s + obj)
            else:
                if unicode:
                    obj = obj.replace("\\", "\\u005c")
                    obj = obj.replace("\n", "\\u000a")
                    obj = obj.encode('raw-unicode-escape')
                    self.write(UNICODE + obj + '\n')
                else:
                    self.write(STRING + repr(obj) + '\n')
            self.memoize(obj) 

def pack_uint(self, x):
        self.__buf.write(struct.pack('>L', x)) 

def pack_float(self, x):
        self.__buf.write(struct.pack('>f', x)) 

def test_ioctl_signed_unsigned_code_param(self):
        if not pty:
            raise unittest.SkipTest('pty module required')
        mfd, sfd = pty.openpty()
        try:
            if termios.TIOCSWINSZ < 0:
                set_winsz_opcode_maybe_neg = termios.TIOCSWINSZ
                set_winsz_opcode_pos = termios.TIOCSWINSZ & 0xffffffffL
            else:
                set_winsz_opcode_pos = termios.TIOCSWINSZ
                set_winsz_opcode_maybe_neg, = struct.unpack("i",
                        struct.pack("I", termios.TIOCSWINSZ))

            our_winsz = struct.pack("HHHH",80,25,0,0)
            # test both with a positive and potentially negative ioctl code
            new_winsz = fcntl.ioctl(mfd, set_winsz_opcode_pos, our_winsz)
            new_winsz = fcntl.ioctl(mfd, set_winsz_opcode_maybe_neg, our_winsz)
        finally:
            os.close(mfd)
            os.close(sfd) 

def test_quick_connect(self):
        # see: http://bugs.python.org/issue10340
        server = TCPServer()
        t = threading.Thread(target=lambda: asyncore.loop(timeout=0.1, count=500))
        t.start()
        self.addCleanup(t.join)

        for x in xrange(20):
            s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            s.settimeout(.2)
            s.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER,
                         struct.pack('ii', 1, 0))
            try:
                s.connect(server.address)
            except socket.error:
                pass
            finally:
                s.close() 

def test_consistence(self):
        self.assertRaises(struct.error, struct.calcsize, 'Z')

        sz = struct.calcsize('i')
        self.assertEqual(sz * 3, struct.calcsize('iii'))

        fmt = 'cbxxxxxxhhhhiillffd?'
        fmt3 = '3c3b18x12h6i6l6f3d3?'
        sz = struct.calcsize(fmt)
        sz3 = struct.calcsize(fmt3)
        self.assertEqual(sz * 3, sz3)

        self.assertRaises(struct.error, struct.pack, 'iii', 3)
        self.assertRaises(struct.error, struct.pack, 'i', 3, 3, 3)
        self.assertRaises((TypeError, struct.error), struct.pack, 'i', 'foo')
        self.assertRaises((TypeError, struct.error), struct.pack, 'P', 'foo')
        self.assertRaises(struct.error, struct.unpack, 'd', 'flap')
        s = struct.pack('ii', 1, 2)
        self.assertRaises(struct.error, struct.unpack, 'iii', s)
        self.assertRaises(struct.error, struct.unpack, 'i', s) 

def test_transitiveness(self):
        c = 'a'
        b = 1
        h = 255
        i = 65535
        l = 65536
        f = 3.1415
        d = 3.1415
        t = True

        for prefix in ('', '@', '<', '>', '=', '!'):
            for format in ('xcbhilfd?', 'xcBHILfd?'):
                format = prefix + format
                s = struct.pack(format, c, b, h, i, l, f, d, t)
                cp, bp, hp, ip, lp, fp, dp, tp = struct.unpack(format, s)
                self.assertEqual(cp, c)
                self.assertEqual(bp, b)
                self.assertEqual(hp, h)
                self.assertEqual(ip, i)
                self.assertEqual(lp, l)
                self.assertEqual(int(100 * fp), int(100 * f))
                self.assertEqual(int(100 * dp), int(100 * d))
                self.assertEqual(tp, t) 

def putmessage(self, message):
        self.debug("putmessage:%d:" % message[0])
        try:
            s = pickle.dumps(message)
        except pickle.PicklingError:
            print >>sys.__stderr__, "Cannot pickle:", repr(message)
            raise
        s = struct.pack("<i", len(s)) + s
        while len(s) > 0:
            try:
                r, w, x = select.select([], [self.sock], [])
                n = self.sock.send(s[:BUFSIZE])
            except (AttributeError, TypeError):
                raise IOError, "socket no longer exists"
            except socket.error:
                raise
            else:
                s = s[n:] 

def gen_subkey(self, K):
        AES_128 = AES.new(K)

        L = AES_128.encrypt('\x00'*16)

        LHigh = unpack('>Q',L[:8])[0]
        LLow  = unpack('>Q',L[8:])[0]

        K1High = ((LHigh << 1) | ( LLow >> 63 )) & 0xFFFFFFFFFFFFFFFF
        K1Low  = (LLow << 1) & 0xFFFFFFFFFFFFFFFF

        if (LHigh >> 63):
            K1Low ^= 0x87

        K2High = ((K1High << 1) | (K1Low >> 63)) & 0xFFFFFFFFFFFFFFFF
        K2Low  = ((K1Low << 1)) & 0xFFFFFFFFFFFFFFFF

        if (K1High >> 63):
            K2Low ^= 0x87

        K1 = pack('>QQ', K1High, K1Low)
        K2 = pack('>QQ', K2High, K2Low)

        return K1, K2 

def setValue(self, settings, e):
        if e.index == 1:
            self.logicalName = _GXCommon.toLogicalName(e.value)
        elif e.index == 2:
            if isinstance(e.value, str):
                self.dataLinkLayerReference = e.value
            else:
                self.dataLinkLayerReference = _GXCommon.toLogicalName(e.value)
        elif e.index == 3:
            self.ipAddress = socket.inet_ntoa(struct.pack("!I", e.value))
        elif e.index == 4:
            self.multicastIPAddress = []
            if e.value:
                for it in e.value:
                    self.multicastIPAddress.append(socket.inet_ntoa(struct.pack("!I", it)))
        elif e.index == 5:
            self.ipOptions = []
            if e.value:
                for it in e.value:
                    item = GXDLMSIp4SetupIpOption()
                    item.type_ = Ip4SetupIpOptionType(it[0])
                    item.length = it[1]
                    item.data = it[2]
                    self.ipOptions.append(item)
        elif e.index == 6:
            self.subnetMask = socket.inet_ntoa(struct.pack("!I", e.value))
        elif e.index == 7:
            self.gatewayIPAddress = socket.inet_ntoa(struct.pack("!I", e.value))
        elif e.index == 8:
            self.useDHCP = e.value
        elif e.index == 9:
            self.primaryDNSAddress = socket.inet_ntoa(struct.pack("!I", e.value))
        elif e.index == 10:
            self.secondaryDNSAddress = socket.inet_ntoa(struct.pack("!I", e.value))
        else:
            e.error = ErrorCode.READ_WRITE_DENIED 

def setFloat(self, value, index=None):
        if index is None:
            self.setFloat(value, self.size)
            self.size += 4
        else:
            self.set(struct.pack("f", value)) 

def setDouble(self, value, index=None):
        if index is None:
            self.setDouble(value, self.size)
            self.size += 8
        else:
            self.set(struct.pack("d", value)) 

def _checkbytes(self, data):
        # CRC is packed in 2 bytes, big-endian
        crc_val = crc.table_driven(map(ord, data))
        crc_str = struct.pack("!H", crc_val)
        # check byte is a modular sum of of the header data
        cb = (sum(map(ord, crc_str + data[:16]))+47)%256
        return chr(cb) + crc_str 

def test_errors(self):
        with self.assertRaisesRegex(RuntimeError, "Magic b'xxx', not "):
            check_magic(io.BytesIO(b'xxx'))
        with self.assertRaisesRegex(RuntimeError, 'we require version 1'):
            check_version(io.BytesIO(b'abcd'))
        with self.assertRaisesRegex(RuntimeError, 'Not enough bytes'):
            file_unpack('<Q', io.BytesIO(b''))

        cmd_header_2_attrs = struct.pack(
            '<IHI',
            2 * (2 + 2 + 3),  # length excluding this header
            CommandKind.MKFILE.value,
            0,  # crc32c
        )

        with self.assertRaisesRegex(RuntimeError, 'CommandHead.* got 0 bytes'):
            read_command(io.BytesIO(cmd_header_2_attrs))

        with self.assertRaisesRegex(RuntimeError, 'AttributeH.* got 0 bytes'):
            read_attribute(io.BytesIO(struct.pack(
                '<HH',
                AttributeKind.PATH.value,
                3,  # length excluding this header -- error: we write no data!
            )))

        with self.assertRaisesRegex(RuntimeError, '\\.PATH occurred twice'):
            read_command(io.BytesIO(cmd_header_2_attrs + struct.pack(
                '<' + 'HH3s' * 2,  # 2 attributes

                AttributeKind.PATH.value,
                3,  # length excluding this header
                b'cat',

                AttributeKind.PATH.value,
                3,  # length excluding this header
                b'dog',
            ))) 

def get_calibrated(self, addr: int):
        return struct.unpack(
            ">f",
            struct.pack(
                "BBBB",
                self.read_reg(addr + 0),
                self.read_reg(addr + 1),
                self.read_reg(addr + 2),
                self.read_reg(addr + 3)))[0] 

def _pack_asf_image(mime, data, type=3, description=""):
    """Pack image data for a WM/Picture tag.
    """
    tag_data = struct.pack('<bi', type, len(data))
    tag_data += mime.encode("utf-16-le") + b'\x00\x00'
    tag_data += description.encode("utf-16-le") + b'\x00\x00'
    tag_data += data
    return tag_data


# iTunes Sound Check encoding. 

def generate():
    "Return the generated output."
    global MESSAGES
    keys = MESSAGES.keys()
    # the keys are sorted in the .mo file
    keys.sort()
    offsets = []
    ids = strs = ''
    for id in keys:
        # For each string, we need size and file offset.  Each string is NUL
        # terminated; the NUL does not count into the size.
        offsets.append((len(ids), len(id), len(strs), len(MESSAGES[id])))
        ids += id + '\0'
        strs += MESSAGES[id] + '\0'
    output = ''
    # The header is 7 32-bit unsigned integers.  We don't use hash tables, so
    # the keys start right after the index tables.
    # translated string.
    keystart = 7*4+16*len(keys)
    # and the values start after the keys
    valuestart = keystart + len(ids)
    koffsets = []
    voffsets = []
    # The string table first has the list of keys, then the list of values.
    # Each entry has first the size of the string, then the file offset.
    for o1, l1, o2, l2 in offsets:
        koffsets += [l1, o1+keystart]
        voffsets += [l2, o2+valuestart]
    offsets = koffsets + voffsets
    output = struct.pack("Iiiiiii",
                         0x950412deL,       # Magic
                         0,                 # Version
                         len(keys),         # # of entries
                         7*4,               # start of key index
                         7*4+len(keys)*8,   # start of value index
                         0, 0)              # size and offset of hash table
    output += array.array("i", offsets).tostring()
    output += ids
    output += strs
    return output 

def _patchheader(self):
        assert self._headerwritten
        if self._datawritten == self._datalength:
            return
        curpos = self._file.tell()
        self._file.seek(self._form_length_pos, 0)
        self._file.write(struct.pack('<L', 36 + self._datawritten))
        self._file.seek(self._data_length_pos, 0)
        self._file.write(struct.pack('<L', self._datawritten))
        self._file.seek(curpos, 0)
        self._datalength = self._datawritten 

def test_endian_short(self):
        if sys.byteorder == "little":
            self.assertIs(c_short.__ctype_le__, c_short)
            self.assertIs(c_short.__ctype_be__.__ctype_le__, c_short)
        else:
            self.assertIs(c_short.__ctype_be__, c_short)
            self.assertIs(c_short.__ctype_le__.__ctype_be__, c_short)
        s = c_short.__ctype_be__(0x1234)
        self.assertEqual(bin(struct.pack(">h", 0x1234)), "1234")
        self.assertEqual(bin(s), "1234")
        self.assertEqual(s.value, 0x1234)

        s = c_short.__ctype_le__(0x1234)
        self.assertEqual(bin(struct.pack("<h", 0x1234)), "3412")
        self.assertEqual(bin(s), "3412")
        self.assertEqual(s.value, 0x1234)

        s = c_ushort.__ctype_be__(0x1234)
        self.assertEqual(bin(struct.pack(">h", 0x1234)), "1234")
        self.assertEqual(bin(s), "1234")
        self.assertEqual(s.value, 0x1234)

        s = c_ushort.__ctype_le__(0x1234)
        self.assertEqual(bin(struct.pack("<h", 0x1234)), "3412")
        self.assertEqual(bin(s), "3412")
        self.assertEqual(s.value, 0x1234) 

def test_endian_int(self):
        if sys.byteorder == "little":
            self.assertIs(c_int.__ctype_le__, c_int)
            self.assertIs(c_int.__ctype_be__.__ctype_le__, c_int)
        else:
            self.assertIs(c_int.__ctype_be__, c_int)
            self.assertIs(c_int.__ctype_le__.__ctype_be__, c_int)

        s = c_int.__ctype_be__(0x12345678)
        self.assertEqual(bin(struct.pack(">i", 0x12345678)), "12345678")
        self.assertEqual(bin(s), "12345678")
        self.assertEqual(s.value, 0x12345678)

        s = c_int.__ctype_le__(0x12345678)
        self.assertEqual(bin(struct.pack("<i", 0x12345678)), "78563412")
        self.assertEqual(bin(s), "78563412")
        self.assertEqual(s.value, 0x12345678)

        s = c_uint.__ctype_be__(0x12345678)
        self.assertEqual(bin(struct.pack(">I", 0x12345678)), "12345678")
        self.assertEqual(bin(s), "12345678")
        self.assertEqual(s.value, 0x12345678)

        s = c_uint.__ctype_le__(0x12345678)
        self.assertEqual(bin(struct.pack("<I", 0x12345678)), "78563412")
        self.assertEqual(bin(s), "78563412")
        self.assertEqual(s.value, 0x12345678) 

def test_unaligned_nonnative_struct_fields(self):
        if sys.byteorder == "little":
            base = BigEndianStructure
            fmt = ">b h xi xd"
        else:
            base = LittleEndianStructure
            fmt = "<b h xi xd"

        class S(base):
            _pack_ = 1
            _fields_ = [("b", c_byte),

                        ("h", c_short),

                        ("_1", c_byte),
                        ("i", c_int),

                        ("_2", c_byte),
                        ("d", c_double)]

        s1 = S()
        s1.b = 0x12
        s1.h = 0x1234
        s1.i = 0x12345678
        s1.d = 3.14
        s2 = struct.pack(fmt, 0x12, 0x1234, 0x12345678, 3.14)
        self.assertEqual(bin(s1), bin(s2)) 

def test_unaligned_native_struct_fields(self):
        if sys.byteorder == "little":
            fmt = "<b h xi xd"
        else:
            base = LittleEndianStructure
            fmt = ">b h xi xd"

        class S(Structure):
            _pack_ = 1
            _fields_ = [("b", c_byte),

                        ("h", c_short),

                        ("_1", c_byte),
                        ("i", c_int),

                        ("_2", c_byte),
                        ("d", c_double)]

        s1 = S()
        s1.b = 0x12
        s1.h = 0x1234
        s1.i = 0x12345678
        s1.d = 3.14
        s2 = struct.pack(fmt, 0x12, 0x1234, 0x12345678, 3.14)
        self.assertEqual(bin(s1), bin(s2)) 

def itn(n, digits=8, format=DEFAULT_FORMAT):
    """Convert a python number to a number field.
    """
    # POSIX 1003.1-1988 requires numbers to be encoded as a string of
    # octal digits followed by a null-byte, this allows values up to
    # (8**(digits-1))-1. GNU tar allows storing numbers greater than
    # that if necessary. A leading 0200 byte indicates this particular
    # encoding, the following digits-1 bytes are a big-endian
    # representation. This allows values up to (256**(digits-1))-1.
    if 0 <= n < 8 ** (digits - 1):
        s = "%0*o" % (digits - 1, n) + NUL
    else:
        if format != GNU_FORMAT or n >= 256 ** (digits - 1):
            raise ValueError("overflow in number field")

        if n < 0:
            # XXX We mimic GNU tar's behaviour with negative numbers,
            # this could raise OverflowError.
            n = struct.unpack("L", struct.pack("l", n))[0]

        s = ""
        for i in xrange(digits - 1):
            s = chr(n & 0377) + s
            n >>= 8
        s = chr(0200) + s
    return s 

def close(self):
        """Close the _Stream object. No operation should be
           done on it afterwards.
        """
        if self.closed:
            return

        if self.mode == "w" and self.comptype != "tar":
            self.buf += self.cmp.flush()

        if self.mode == "w" and self.buf:
            self.fileobj.write(self.buf)
            self.buf = ""
            if self.comptype == "gz":
                # The native zlib crc is an unsigned 32-bit integer, but
                # the Python wrapper implicitly casts that to a signed C
                # long.  So, on a 32-bit box self.crc may "look negative",
                # while the same crc on a 64-bit box may "look positive".
                # To avoid irksome warnings from the `struct` module, force
                # it to look positive on all boxes.
                self.fileobj.write(struct.pack("<L", self.crc & 0xffffffffL))
                self.fileobj.write(struct.pack("<L", self.pos & 0xffffFFFFL))

        if not self._extfileobj:
            self.fileobj.close()

        self.closed = True 

def _create_header(info, format):
        """Return a header block. info is a dictionary with file
           information, format must be one of the *_FORMAT constants.
        """
        parts = [
            stn(info.get("name", ""), 100),
            itn(info.get("mode", 0) & 07777, 8, format),
            itn(info.get("uid", 0), 8, format),
            itn(info.get("gid", 0), 8, format),
            itn(info.get("size", 0), 12, format),
            itn(info.get("mtime", 0), 12, format),
            "        ", # checksum field
            info.get("type", REGTYPE),
            stn(info.get("linkname", ""), 100),
            stn(info.get("magic", POSIX_MAGIC), 8),
            stn(info.get("uname", ""), 32),
            stn(info.get("gname", ""), 32),
            itn(info.get("devmajor", 0), 8, format),
            itn(info.get("devminor", 0), 8, format),
            stn(info.get("prefix", ""), 155)
        ]

        buf = struct.pack("%ds" % BLOCKSIZE, "".join(parts))
        chksum = calc_chksums(buf[-BLOCKSIZE:])[0]
        buf = buf[:-364] + "%06o\0" % chksum + buf[-357:]
        return buf 

def _writeinfo(self, name, finfo):
        nl = len(name)
        if nl > 63:
            raise Error, 'Filename too long'
        d = chr(nl) + name + '\0'
        d2 = finfo.Type + finfo.Creator

        # Force all structs to be packed with big-endian
        d3 = struct.pack('>h', finfo.Flags)
        d4 = struct.pack('>ii', self.dlen, self.rlen)
        info = d + d2 + d3 + d4
        self._write(info)
        self._writecrc() 

def _writecrc(self):
        # XXXX Should this be here??
        # self.crc = binascii.crc_hqx('\0\0', self.crc)
        if self.crc < 0:
            fmt = '>h'
        else:
            fmt = '>H'
        self.ofp.write(struct.pack(fmt, self.crc))
        self.crc = 0 

def get(self, i, pack=struct.pack):
        if self.bin:
            if i < 256:
                return BINGET + chr(i)
            else:
                return LONG_BINGET + pack("<i", i)

        return GET + repr(i) + '\n' 

def save_long(self, obj, pack=struct.pack):
        if self.proto >= 2:
            bytes = encode_long(obj)
            n = len(bytes)
            if n < 256:
                self.write(LONG1 + chr(n) + bytes)
            else:
                self.write(LONG4 + pack("<i", n) + bytes)
            return
        self.write(LONG + repr(obj) + '\n') 

def save_float(self, obj, pack=struct.pack):
        if self.bin:
            self.write(BINFLOAT + pack('>d', obj))
        else:
            self.write(FLOAT + repr(obj) + '\n') 

def save_string(self, obj, pack=struct.pack):
        if self.bin:
            n = len(obj)
            if n < 256:
                self.write(SHORT_BINSTRING + chr(n) + obj)
            else:
                self.write(BINSTRING + pack("<i", n) + obj)
        else:
            self.write(STRING + repr(obj) + '\n')
        self.memoize(obj) 

def save_global(self, obj, name=None, pack=struct.pack):
        write = self.write
        memo = self.memo

        if name is None:
            name = obj.__name__

        module = getattr(obj, "__module__", None)
        if module is None:
            module = whichmodule(obj, name)

        try:
            __import__(module)
            mod = sys.modules[module]
            klass = getattr(mod, name)
        except (ImportError, KeyError, AttributeError):
            raise PicklingError(
                "Can't pickle %r: it's not found as %s.%s" %
                (obj, module, name))
        else:
            if klass is not obj:
                raise PicklingError(
                    "Can't pickle %r: it's not the same object as %s.%s" %
                    (obj, module, name))

        if self.proto >= 2:
            code = _extension_registry.get((module, name))
            if code:
                assert code > 0
                if code <= 0xff:
                    write(EXT1 + chr(code))
                elif code <= 0xffff:
                    write("%c%c%c" % (EXT2, code&0xff, code>>8))
                else:
                    write(EXT4 + pack("<i", code))
                return

        write(GLOBAL + module + '\n' + name + '\n')
        self.memoize(obj) 

def _write_short(f, x):
    f.write(struct.pack('>h', x)) 

def _write_ushort(f, x):
    f.write(struct.pack('>H', x)) 

def _write_long(f, x):
    f.write(struct.pack('>l', x)) 

def _write_string(f, s):
    if len(s) > 255:
        raise ValueError("string exceeds maximum pstring length")
    f.write(struct.pack('B', len(s)))
    f.write(s)
    if len(s) & 1 == 0:
        f.write(chr(0)) 

def write32u(output, value):
    # The L format writes the bit pattern correctly whether signed
    # or unsigned.
    output.write(struct.pack("<L", value)) 

def FileHeader(self, zip64=None):
        """Return the per-file header as a string."""
        dt = self.date_time
        dosdate = (dt[0] - 1980) << 9 | dt[1] << 5 | dt[2]
        dostime = dt[3] << 11 | dt[4] << 5 | (dt[5] // 2)
        if self.flag_bits & 0x08:
            # Set these to zero because we write them after the file data
            CRC = compress_size = file_size = 0
        else:
            CRC = self.CRC
            compress_size = self.compress_size
            file_size = self.file_size

        extra = self.extra

        if zip64 is None:
            zip64 = file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT
        if zip64:
            fmt = '<HHQQ'
            extra = extra + struct.pack(fmt,
                    1, struct.calcsize(fmt)-4, file_size, compress_size)
        if file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT:
            if not zip64:
                raise LargeZipFile("Filesize would require ZIP64 extensions")
            # File is larger than what fits into a 4 byte integer,
            # fall back to the ZIP64 extension
            file_size = 0xffffffff
            compress_size = 0xffffffff
            self.extract_version = max(45, self.extract_version)
            self.create_version = max(45, self.extract_version)

        filename, flag_bits = self._encodeFilenameFlags()
        header = struct.pack(structFileHeader, stringFileHeader,
                 self.extract_version, self.reserved, flag_bits,
                 self.compress_type, dostime, dosdate, CRC,
                 compress_size, file_size,
                 len(filename), len(extra))
        return header + filename + extra 

def pack_double(self, x):
        self.__buf.write(struct.pack('>d', x)) 

def make_pyc(co, mtime):
    data = marshal.dumps(co)
    if type(mtime) is type(0.0):
        # Mac mtimes need a bit of special casing
        if mtime < 0x7fffffff:
            mtime = int(mtime)
        else:
            mtime = int(-0x100000000L + long(mtime))
    pyc = imp.get_magic() + struct.pack("<i", int(mtime)) + data
    return pyc 

def _testBogusZipFile(self):
        test_support.unlink(TESTMOD)
        fp = open(TESTMOD, 'w+')
        fp.write(struct.pack('=I', 0x06054B50))
        fp.write('a' * 18)
        fp.close()
        z = zipimport.zipimporter(TESTMOD)

        try:
            self.assertRaises(TypeError, z.find_module, None)
            self.assertRaises(TypeError, z.load_module, None)
            self.assertRaises(TypeError, z.is_package, None)
            self.assertRaises(TypeError, z.get_code, None)
            self.assertRaises(TypeError, z.get_data, None)
            self.assertRaises(TypeError, z.get_source, None)

            error = zipimport.ZipImportError
            self.assertEqual(z.find_module('abc'), None)

            self.assertRaises(error, z.load_module, 'abc')
            self.assertRaises(error, z.get_code, 'abc')
            self.assertRaises(IOError, z.get_data, 'abc')
            self.assertRaises(error, z.get_source, 'abc')
            self.assertRaises(error, z.is_package, 'abc')
        finally:
            zipimport._zip_directory_cache.clear() 

def to_ulps(x):
    """Convert a non-NaN float x to an integer, in such a way that
    adjacent floats are converted to adjacent integers.  Then
    abs(ulps(x) - ulps(y)) gives the difference in ulps between two
    floats.

    The results from this function will only make sense on platforms
    where C doubles are represented in IEEE 754 binary64 format.

    """
    n = struct.unpack('<q', struct.pack('<d', x))[0]
    if n < 0:
        n = ~(n+2**63)
    return n