This question is probably very easy for most of you, but i cant find the answer so far.

I'm building a network packet generator that goes like this:

class PacketHeader(Packet):
fields = OrderedDict([("head", "\x00"),("headpad", "\x00"),("headlen", "\x1a\x00" ),("presentflag", "\x2e"),("timestamp", "\x43\x10\x58\x16\xa1\x01\x00\x00"),("flag", "\x03"),("Sequencenum", "\x04\x00"),])

Later, I call my class and send the packet like this:

send(PacketHeader(Sequencenum=257))
send(PacketHeader(Sequencenum=258))
send(PacketHeader(Sequencenum=259))

Unfortunatly, on the wire i have \x32\x35\x37 (257 in hex) instead of having this :\x01\x01.

What i would like to do, is being able to:

send(PacketHeader(Sequencenum=257+1)) 

and have it converted to int correctly on the wire

Thanks in advance !

If you want to convert int or any other primitive data type to binary then the struct module might help you.

http://docs.python.org/library/struct

>>> import struct
>>> struct.pack('>i', 257)
'\x00\x00\x01\x01'
>>> struct.pack('<i', 257)
'\x01\x01\x00\x00'
>>> struct.unpack('<i', '\x01\x01\x00\x00')
(257,)
>>> struct.unpack('>i', '\x00\x00\x01\x01')
(257,)

ms4py mentioned you might want to convert 2 byte ints so:

>>> struct.pack('>h', 257)
'\x01\x01'
>>> struct.unpack('>h', '\x01\x01')
(257,)
>>> 

oh and:

>>> struct.unpack('>h', '\x10\x00')
(4096,)
>>>