How can I encode a 32bit integer into a byte array?

Question

I'm required to send a 32bit integer over a serial connection like so: 0xc6bf6f34 should become: b'\xc6\xbf\x6f\x34'.

To that end, I created this, but, as always after such coding, I wondered if it's pythonicism could be improved with something in the standard libary:

def ltonlba(value):
    ''' ltonlba : Long to Network Long Byte Array '''
    from socket import htonl
    value = htonl(value)
    ba = b''
    for i in range(4):
            ba += chr((value) & 0xff)
            value >>= 8
    return ba

falsetru · Accepted Answer · 2017-06-15 15:27:30Z

6

If you're using Python 3.2+, you can use int.to_bytes:

>>> 0xc6bf6f34.to_bytes(4, 'little')  # 4 bytes = 32 bits
b'4o\xbf\xc6'
>>> 0xc6bf6f34.to_bytes(4, 'little') == b'\x34\x6f\xbf\xc6'
True

Otherwise, you can use struct.pack with <I format (<: little-endian, I: 4-bytes unsigned integer , see Format strings - struct module doc):

>>> import struct
>>> struct.pack('<I', 0xc6bf6f34)
b'4o\xbf\xc6'

UPDATE / NOTE: If you want to get big-endian (or network-endian), you should specify 'big' with int.to_bytes:

0xc6bf6f34.to_bytes(4, 'big')  # == b'\xc6\xbf\x6f\x34'

and > or ! with struct.pack:

struct.pack('>I', 0xc6bf6f34)  # == b'\xc6\xbf\x6f\x34'  big-endian
struct.pack('!I', 0xc6bf6f34)  # == b'\xc6\xbf\x6f\x34'  network (= big-endian)

edited Jun 15, 2017 at 15:27

answered Jun 15, 2017 at 15:15

falsetru

371k69 gold badges769 silver badges659 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Jamie Over a year ago

Does the struct.pack() solution work with Python 3.2+ as well?

falsetru Over a year ago

@Jamie, It works with both in Python 2.x, 3.x. I tested it in Python 2.7.13 / 3.5.3 / 3.6.1.

falsetru Over a year ago

@Jamie, I rolled back your change. You want little little-endian according to your question.

falsetru Over a year ago

@Jamie, If you specify network-endian (or big-endian) , you will get b\xc6\xbf\x6f\x34 instead.

falsetru Over a year ago

@Jamie, I updated the answer to explicitly mention it.

Collectives™ on Stack Overflow

How can I encode a 32bit integer into a byte array?

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related