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I have a long Hex string that represents a series of values of different types. I wish to convert this Hex String into a byte array so that I can shift each value out and convert it into its proper data type.

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How does that hex string look like? – khachik Apr 13 '11 at 12:46
1  
There is a big difference between hexidecimal and hexadecimal - you might want to fix your title! – Steve Folly Apr 13 '11 at 13:34
@Steve Folly good catch – Richard Apr 13 '11 at 14:23

6 Answers

up vote 15 down vote accepted

Suppose your hex string is something like "deadbeef".

"deadbeef"

Convert it to a string:

result= hex_string.decode("hex")

Convert it to a byte array:

import array
result= array.array('B', hex_string.decode("hex"))

Convert it to a list of byte values:

result= map(ord, hex_string.decode("hex"))

or, possibly:

result= bytearray(hex_string.decode("hex"))

if on a recent enough Python.
_

However, it's possible that by “hex string” you just mean a string with unprintable characters.

"\x12\x45\x00AB"

In that case, use the options above ignoring the .decode("hex") part.

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up vote 9 down vote

There is a built-in function in bytearray that does what you intend.

bytearray.fromhex("de ad be ef 00")

It returns a bytearray and it reads hex strings with or without space separator.

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up vote 2 down vote

provided I understood correctly, you should look for binascii.unhexlify

import binascii
a='45222e'
s=binascii.unhexlify(a)
b=[ord(x) for x in s]
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I agree that unhexlify is the most efficient way to go here, but would suggest that b = bytearray(s) would be a better than using ord. As Python has a built-in type just for arrays of bytes I'm surprised no one is using it – Scott Griffiths Apr 13 '11 at 15:03
up vote 0 down vote

You should be able to build a string holding the binary data using something like:

data = "fef0babe"
bits = ""
for x in xrange(0, len(data), 2)
  bits += chr(int(data[x:x+2], 16))

This is probably not the fastest way (many string appends), but quite simple using only core Python.

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up vote 0 down vote

Assuming you have a byte string like so

"\x12\x45\x00\xAB"

and you know the amount of bytes and their type you can also use this approach

import struct

bytes = '\x12\x45\x00\xAB'
val = struct.unpack('<BBH', bytes)

#val = (18, 69, 43776)

As I specified little endian (using the '<' char) at the start of the format string the function returned the decimal equivalent.

0x12 = 18

0x45 = 69

0xAB00 = 43776

B is equal to one byte (8 bit) unsigned

H is equal to two bytes (16 bit) unsigned

More available characters and byte sizes can be found here

The advantages are..

You can specify more than one byte and the endian of the values

Disadvantages..

You really need to know the type and length of data your dealing with

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up vote -1 down vote

A good one liner is:

byte_list = map(ord, hex_string)

This will iterate over each char in the string and run it through the ord() function. Only tested on python 2.6, not too sure about 3.0+.

-Josh

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perfect. Working on python 2.7 – Richard Apr 13 '11 at 13:06
Click the outline of the checkmark next to this answer if it's the right one! :) – jathanism Apr 13 '11 at 13:54
2  
This converts to a list of codepoints, not a bytearray. – Glenn Maynard Apr 13 '11 at 15:00
This doesn't convert hex - it converts each character of a string to an integer. For hex each pair of characters would represent a byte. You might as well just say byte_list = bytearray(hex_string) – Scott Griffiths Apr 13 '11 at 15:11

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