How can I represent a byte array (like in Java with byte[]) in Python? I'll need to send it over the wire with gevent.
byte key[] = {0x13, 0x00, 0x00, 0x00, 0x08, 0x00};
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4 Answers
In Python 3, we use the bytes object, also known as str in Python 2.
# Python 3
key = bytes([0x13, 0x00, 0x00, 0x00, 0x08, 0x00])
# Python 2
key = ''.join(chr(x) for x in [0x13, 0x00, 0x00, 0x00, 0x08, 0x00])
I find it more convenient to use the base64 module...
# Python 3
key = base64.b16decode(b'130000000800')
# Python 2
key = base64.b16decode('130000000800')
You can also use literals...
# Python 3
key = b'\x13\0\0\0\x08\0'
# Python 2
key = '\x13\0\0\0\x08\0'
2 Comments
Dolda2000
For the record, instead of
base64.b16decode(x), you can use, simply, x.decode("hex"). It lets you get by with one less import, at least. :)
Mark Tolonen
bytes.fromhex('130000000800') in Python 3.Just use a bytearray (Python 2.6 and later) which represents a mutable sequence of bytes
>>> key = bytearray([0x13, 0x00, 0x00, 0x00, 0x08, 0x00])
>>> key
bytearray(b'\x13\x00\x00\x00\x08\x00')
Indexing get and sets the individual bytes
>>> key[0]
19
>>> key[1]=0xff
>>> key
bytearray(b'\x13\xff\x00\x00\x08\x00')
and if you need it as a str (or bytes in Python 3), it's as simple as
>>> bytes(key)
'\x13\xff\x00\x00\x08\x00'
3 Comments
John Machin
Not so simple with 3.x;
fubar = str(key); print(len(key), len(fubar)) produces 6 38. In any case (1) "string" is very vague terminology (2) if he wants mutability, he can mutate his original list
Scott Griffiths
@John: Good point about
str working differently for bytearray in Python 3 - fixed. I mentioned mutability mainly to distinguish it from bytes, but the point is also that you don't need to have an intermediate step of having your data in a list at all.John Machin
It's a fair chance that what the OP really needs is something like
struct.pack("<IH", 19, 8) ...An alternative that also has the added benefit of easily logging its output:
hexs = "13 00 00 00 08 00"
logging.debug(hexs)
key = bytearray.fromhex(hexs)
allows you to do easy substitutions like so:
hexs = "13 00 00 00 08 {:02X}".format(someByte)
logging.debug(hexs)
key = bytearray.fromhex(hexs)
Comments
Dietrich's answer is probably just the thing you need for what you describe, sending bytes, but a closer analogue to the code you've provided for example would be using the bytearray type.
>>> key = bytearray([0x13, 0x00, 0x00, 0x00, 0x08, 0x00])
>>> bytes(key)
b'\x13\x00\x00\x00\x08\x00'
>>>
answered Sep 11, 2011 at 18:58
SingleNegationElimination
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3 Comments
Scott Griffiths
Fine for Python 2.5 or earlier, but the built-in
bytearray is really the way to go if you want, er, a byte array.John Machin
@TokenMacGuy: Your answer needs another 2 edits: (1) mentions the array module (2)
bytearray('b', ...) doesn't work. Or you could just delete it.
SingleNegationElimination
@John: thanks, fixed. In the future, just go right ahead and make the edits yourself.