int to binary python

Question

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 !

I'm confused by perhaps too much information :-) Are you trying to convert an integer to hex? Can you give a simple input and desired output example? — Levon
– Levon, Commented Jul 10, 2012 at 20:54
@martineau: My mistake, you should have read : "\x01\x01". Will modify my post. — user1473508
– user1473508, Commented Jul 10, 2012 at 22:00

Samy Vilar · Accepted Answer · 2012-07-10 21:22:47Z

3

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,)
>>>

edited Jul 10, 2012 at 21:22

answered Jul 10, 2012 at 20:55

Samy Vilar

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3 Comments

schlamar Over a year ago

Probably he wants a short (two bytes for an int): >>> struct.pack('!h', 258) '\x01\x02'

Samy Vilar Over a year ago

maybe your right, I have no idea :( ... either way the link to the struct should help him decide how he wants to do the conversion, I'll add the example anyway, thank you.

user1473508 Over a year ago

I should have thought about this !! Thanks for your answer.

Jon Clements · Accepted Answer · 2012-07-10 20:57:31Z

0

If you have an integer and want hex:

hex(257)
'0x101'

Other way around

int('0x101', 16)
257

answered Jul 10, 2012 at 20:57

Jon Clements

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4 Comments

Levon Over a year ago

That's what I thought too .. but seems almost too straight forward :) Maybe OP will clarify

Jon Clements Over a year ago

@Levon Agreed - but figured I'd take a punt ;)

Levon Over a year ago

Who knows, this may just be the ticket .. you'll get my upvote too if OP likes it.

Jon Clements Over a year ago

@Levon I do like the struct answer though - more portable

inspectorG4dget · Accepted Answer · 2012-07-10 21:03:00Z

-1

Seems to me, that you want an integer to binary converter.

If that's the case, then this should work:

def convert(N):
    if not N:
        return ''
    else:
        return "%s%s" %(convert(N/2), N%2)

Hope this helps

answered Jul 10, 2012 at 21:03

inspectorG4dget

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4 Comments

Levon Over a year ago

bin(N)[2:] will already do that :) .. " batteries included" and all that. (didn't downvote!)

inspectorG4dget Over a year ago

did NOT know about bin(n). Oh God! the number of times I've done this! I've wasted so many LOC in so many modules over the years sheds a silent tear

Jon Clements Over a year ago

@Levon the code is the same as '{:b}'.format(257) I think (if you don't want the leading 0x stuff...)

inspectorG4dget Over a year ago

Downvoter: Would you like to give me a reason so I can upgrade my answer?

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