How to convert string to byte array in Python

Question

Say that I have a 4 character string, and I want to convert this string into a byte array where each character in the string is translated into its hex equivalent. e.g.

str = "ABCD"

I'm trying to get my output to be

array('B', [41, 42, 43, 44])

Is there a straightforward way to accomplish this?

What you want is not possible, at least not in this exact form. A bytearray of type `B` contains 1-byte integers, and they are always represented in decimal. — Tim Pietzcker, Jul 24 '12 at 04:50

avasal · Accepted Answer · 2012-07-24T09:06:54.697

66

encode function can help you here, encode returns an encoded version of the string

In [44]: str = "ABCD"

In [45]: [elem.encode("hex") for elem in str]
Out[45]: ['41', '42', '43', '44']

or you can use array module

In [49]: import array

In [50]: print array.array('B', "ABCD")
array('B', [65, 66, 67, 68])

edited Jul 24 '12 at 09:06

answered Jul 24 '12 at 04:39

avasal

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however as you can see,, array module gives a ascii value of string elements, which doesn't match with your expected output – avasal Jul 24 '12 at 04:51
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This is the accepted answer and does not work in Python3. Could you please add the python3 version as pointed in other answers? – Fabio Picchi Oct 24 '18 at 14:14

Pithikos · Answer 2 · 2015-04-13T15:29:10.197

66

Just use a bytearray() which is a list of bytes.

Python2:

s = "ABCD"
b = bytearray()
b.extend(s)

Python3:

s = "ABCD"
b = bytearray()
b.extend(map(ord, s))

By the way, don't use str as a variable name since that is builtin.

edited Apr 13 '15 at 15:29

answered Mar 20 '15 at 14:32

Pithikos

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This is broken in 3.4: `TypeError: an integer is required` – Kevan Ahlquist Apr 10 '15 at 02:43
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@KevanAhlquist my bad. Fixed it now. – Pithikos Apr 13 '15 at 15:29
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For Python 3 this looks cleaner to me: `s = "ABCD"`, `b = bytearray()`, `b.extend(s.encode())` – Diego Herranz Jun 15 '16 at 16:53
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Regarding [encode()](https://docs.python.org/3.4/library/stdtypes.html#str.encode), it returns a bytes object which naturally extends a bytearray. – Diego Herranz Jun 15 '16 at 17:00
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`map(ord, s)` will return values > 255 unless your strings are strictly ASCII. Please update your answer to include something like `s.encode('utf-8')`. (Note that UTF-8 is a strict superset of ASCII, so it does not alter ASCII strings in any way.) – 9000 Feb 14 '18 at 20:54
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@9000 it is incorrect to use `.encode()` as well as `.encode('utf-8')`. Use `map(ord, ...)` if you don't want you bytes to be transformed. https://repl.it/repls/MistySubtleVisitors just press `run` and see the result. – user70960 Mar 18 '20 at 13:26
in my use case (socket send), only `b.extend(map(ord, s))` works, none of the following works: `s.encode(), s.encode(‘ascii’), bytearray(s.encode())` – ios learner Mar 02 '21 at 23:47

score 24 · Answer 3 · edited Jul 19 '15 at 13:57

24

An alternative to get a byte array is to encode the string in ascii: b=s.encode('ascii').

edited Jul 19 '15 at 13:57

josliber

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answered Jul 19 '15 at 06:42

Jon Perryman

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Assuming that the string is ASCII to begin with. If you have s = '\x80', that's not going to work. – FuriousGeorge Jul 31 '21 at 01:23
what if s = '\x80' what then to do? – mbrc Sep 14 '21 at 08:05

score 13 · Answer 4 · edited Jun 22 '21 at 20:43

13

Depending on your needs, this can be one step or two steps

use encode() to convert string to bytes, immutable
use bytearray() to convert bytes to bytearray, mutable

s="ABCD"
encoded=s.encode('utf-8')
array=bytearray(encoded)

The following validation is done in Python 3.7

>>> s="ABCD"
>>> encoded=s.encode('utf-8')
>>> encoded
b'ABCD'
>>> array=bytearray(encoded)
>>> array
bytearray(b'ABCD')

edited Jun 22 '21 at 20:43

Lleims

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answered Aug 01 '20 at 23:45

oldpride

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It helped me in some other thing. Thanks – ABD Aug 23 '22 at 13:19

mgear · Answer 5 · 2020-06-03T14:29:36.100

10

This works for me (Python 2)

s = "ABCD"
b = bytearray(s)

# if you print whole b, it still displays it as if its original string
print b

# but print first item from the array to see byte value
print b[0]

Reference: http://www.dotnetperls.com/bytes-python

edited Jun 03 '20 at 14:29

answered May 27 '16 at 03:13

mgear

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juliocesar · Answer 6 · 2019-08-10T14:29:00.590

9

This work in both Python 2 and 3:

>>> bytearray(b'ABCD')
bytearray(b'ABCD')

Note string started with b.

To get individual chars:

>>> print("DEC HEX ASC")
... for b in bytearray(b'ABCD'):
...     print(b, hex(b), chr(b))
DEC HEX ASC
65 0x41 A
66 0x42 B
67 0x43 C
68 0x44 D

Hope this helps

edited Aug 10 '19 at 14:29

answered Apr 22 '19 at 17:17

juliocesar

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score 1 · Answer 7 · edited Jul 24 '12 at 05:19

1

s = "ABCD"
from array import array
a = array("B", s)

If you want hex:

print map(hex, a)

edited Jul 24 '12 at 05:19

Anthony

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answered Jul 24 '12 at 04:51

HYRY

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Does not work in repl.it. Returns: "TypeError: cannot use a str to initialize an array with typecode 'B' " – MikeB2019x Mar 12 '20 at 14:22

score 1 · Answer 8 · answered Dec 15 '21 at 14:04

Since none of the answers is producing exactly array('B', [41, 42, 43, 44]) and the answer by avasal fails in Python 3, I post here my alternative:

import array
s = 'ABCD'
a = array.array('B', [ord(c) for c in s])
print(a)

which prints

array('B', [65, 66, 67, 68])

Note that 65-68 is the correct ASCII for "ABCD".

score -1 · Answer 9 · edited Dec 19 '18 at 15:19

-1

for python 3 it worked for what @HYRY posted. I needed it for a returned data in a dbus.array. This is the only way it worked

s = "ABCD"

from array import array

a = array("B", s)

edited Dec 19 '18 at 15:19

Zoe

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answered Dec 19 '18 at 15:08

July Marval

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How to convert string to byte array in Python

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