Bytes representation in Python

Question

I need to do some work with bytes in Python and I've come across a byte string I don't really understand:

b"H\x00\x84\xffQ\x00\xa6\xff+\x00\x96\xff\xc2\xffI\xff\xa5\xff'\xff\x8a\xff\x19\xff\x19\xff\xf6\xfe\xb0\xfe\xc7\xfeJ\xfel\xfe\xf8\xfd+\xfe\xef\xfd:\xfe\xc3\xfd*\xfe_\xfd\xdf\xfd\n\xfd\xa3\xfd\xc6\xfcq\xfd\xbd\xfc?\xfd"

So according to what I know, bytes should be represented as \xhh, where hh are hexadecimal values (from 0 to f). However, in the third segment, there is \xffQ, and farther on there are other characters which shouldn't appear: I, ', *, :, ? etc. I've used hex() method to see what would be the outcome, and I got this:

480084ff5100a6ff2b0096ffc2ff49ffa5ff27ff8aff19ff19fff6feb0fec7fe4afe6cfef8fd2bfeeffd3afec3fd2afe5ffddffd0afda3fdc6fc71fdbdfc3ffd

As you can see, some parts of the hex are the same, but e.g. \xffQ was changed into ff51. I need to append some data to this byte string, so I'd like to know what's going on there (or how to get the same result).

Only unprintable characters are encoded using \x__, others are just shown as ASCII characters. — tkausl
– tkausl, Commented Aug 6, 2022 at 15:06
bytes are represented in printable characters where possible. 0x51 is the ASCII value for Q. — sj95126
– sj95126, Commented Aug 6, 2022 at 15:07
If there's a canonical answer for this, I can't find it, but this question does come up periodically (ex.: recent question I answered) — sj95126
– sj95126, Commented Aug 6, 2022 at 15:24

jackal · Accepted Answer · 2022-08-06 15:13:19Z

1

Both repr and str when processing a bytes object will print ASCII characters where possible. Otherwise their hexadecimal values will be shown in the form \xNN.

It might help you to visualise the content if you print it as all hexadecimal as follows:

b = b"H\x00\x84\xffQ\x00\xa6\xff+\x00\x96\xff\xc2\xffI\xff\xa5\xff'\xff\x8a\xff\x19\xff\x19\xff\xf6\xfe\xb0\xfe\xc7\xfeJ\xfel\xfe\xf8\xfd+\xfe\xef\xfd:\xfe\xc3\xfd*\xfe_\xfd\xdf\xfd\n\xfd\xa3\xfd\xc6\xfcq\xfd\xbd\xfc?\xfd"
print(''.join(hex(b_) for b_ in b))

Output:

0x480x00x840xff0x510x00xa60xff0x2b0x00x960xff0xc20xff0x490xff0xa50xff0x270xff0x8a0xff0x190xff0x190xff0xf60xfe0xb00xfe0xc70xfe0x4a0xfe0x6c0xfe0xf80xfd0x2b0xfe0xef0xfd0x3a0xfe0xc30xfd0x2a0xfe0x5f0xfd0xdf0xfd0xa0xfd0xa30xfd0xc60xfc0x710xfd0xbd0xfc0x3f0xfd

answered Aug 6, 2022 at 15:13

jackal

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funnydman · Accepted Answer · 2022-08-06 15:31:21Z

1

Or you can use binascii module if you want to visualize the content:

import binascii 
print(binascii.hexlify(b"hello world"))

Output:

68656c6c6f20776f726c64

answered Aug 6, 2022 at 15:31

funnydman

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