python 2.7 equivalent of built-in method int.from_bytes

Question

I'm trying to make my project python2.7 and 3 compatible and python 3 has the built in method int.from_bytes. Does the equivalent exist in python 2.7 or rather what would be the best way to make this code 2.7 and 3 compatible?

>>> int.from_bytes(b"f483", byteorder="big")
1714698291

If you're specifically looking for a cross-version solution then you should make this clear in the title. — Ignacio Vazquez-Abrams
– Ignacio Vazquez-Abrams, Commented May 22, 2015 at 17:45

dawg · Accepted Answer · 2015-05-22 18:24:43Z

29

You can treat it as an encoding (Python 2 specific):

>>> int('f483'.encode('hex'), 16)
1714698291

Or in Python 2 and Python 3:

>>> int(codecs.encode(b'f483', 'hex'), 16)
1714698291

The advantage is the string is not limited to a specific size assumption. The disadvantage is it is unsigned.

edited May 22, 2015 at 18:24

answered May 22, 2015 at 18:09

dawg

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4 Comments

Joran Beasley Over a year ago

hah I like this solution ... alot ... its one I would not have thought of :) it has the added advantage of not having to know anything about the input

dawg Over a year ago

Yours is better really cause it should work in Python 2 and 3. Thanks tho

vonec Over a year ago

What would be the reverse of this? I'd like to retrieve the original byte string from the integer

deed02392 Over a year ago

What about ord(b'\x11')?

Joran Beasley · Accepted Answer · 2015-05-22 18:09:50Z

12

struct.unpack(">i","f483")[0]

maybe?

> means big-endian and i means signed 32 bit int

see also: https://docs.python.org/2/library/struct.html

edited May 22, 2015 at 18:09

answered May 22, 2015 at 17:39

Joran Beasley

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2 Comments

Janus Troelsen Over a year ago

it won't work for anything bigger than int32 of course. any hints?

Tatarize Over a year ago

When the bytes is less than 4 this won't work, when it would have worked for int.from_bytes()

SanketDG · Accepted Answer · 2015-05-22 19:29:44Z

6

Use the struct module to unpack your bytes into integers.

import struct
>>> struct.unpack("<L", "y\xcc\xa6\xbb")[0]
3148270713L

edited May 22, 2015 at 19:29

answered May 22, 2015 at 17:55

SanketDG

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2 Comments

Joran Beasley Over a year ago

that just unpacks them into bytes ... he wants them all as 1 32 bit integer ... maybe bigger ... but you are right that stuct is the module to use :)

SanketDG Over a year ago

I didn't realize he needed the actual integer values, but yeah, fixed.

Martel · Accepted Answer · 2019-04-04 10:06:18Z

1

> import binascii

> barray = bytearray([0xAB, 0xCD, 0xEF])
> n = int(binascii.hexlify(barray), 16)
> print("0x%02X" % n)

0xABCDEF

answered Apr 4, 2019 at 10:06

Martel

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Comments

ewerybody · Accepted Answer · 2025-02-13 11:39:23Z

0

I was looking for a 2.7 version that works with signed integers from 8 chars wide hex strings, so also negative numbers and came up with this using struct:

>>> import struct

>>> n = 'ffffffd6'
>>> struct.unpack(">l", n.decode('hex'))[0]
-42

>>> n4 = 'ffd6'
>>> struct.unpack(">h", n4.decode('hex'))[0]
-42

answered Feb 13 at 11:39

ewerybody

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