python read binary file byte by byte

Question

This might seem pretty stupid, but I'm a complete newbie in python.

So, I have a binary file that starts by

ff d8 ff e0 00 10 4a

(as seen both through Hex Editor Neo and a java program)

yet, when I tried to read it with python by

with open(absolutePathInput, "rb") as f:
    while True:
        current_byte = f.read(1)
        if(not current_byte):
            break
        print(hex(current_byte[0]))

I get

ff d8 ff e0 0 10 31

It seems that it goes wrong whenever the first 0x00 is readen.

what am I doing wrong? Thank u!

Are you asking about why it keeps reading past the null byte, or why it only prints 0 instead of 00? (It should be printing 0x in front of all these hex representations, and it should be printing them on separate lines; it looks like you edited the output. Please don't do that.) — user2357112
– user2357112, Commented May 18, 2017 at 22:26
What do you mean by "goes wrong"? It doesn't print what you want? It doesn't break when you want it to? What to you want to happen? — tdelaney
– tdelaney, Commented May 18, 2017 at 22:29
You should get a similar result with any byte with a leading zero. — chepner
– chepner, Commented May 18, 2017 at 22:33
-Since I stated before, I'm reading a binary file , so, no, I'm obviously not asking why it keeps reading past the null byte. -Though this is not as obvious, since I'm reading binary data, I'm not concerned why the print() prints 0x0 instead of 0x00. -What I'm concerned about is why it reads 0x31 instead of 0x4a — glezo
– glezo, Commented May 19, 2017 at 7:42
certainly, you may: b'\xff\xd8\xff\xe0\x00\x10130y' That's my issue: dispite the fact I want to read byte by byte, I don't understand why it's reading as if it was utf-8. I guess I have to specify a certain encoding to the open(), but I dunno which one. — glezo
– glezo, Commented May 19, 2017 at 11:51

slashdottir · Accepted Answer · 2017-06-13 21:39:15Z

2

I think the issue is you are trying to dereference current_byte as though it were an array, but it is simply a byte

def test_write_bin(self):  
  fname = 'test.bin'
  f = open(fname, 'wb')
  # ff d8 ff e0 00 10 4a
  f.write(bytearray([255, 216, 255, 224, 0, 16, 74]))
  f.close()
  with open(fname, "rb") as f2:
    while True:
      current_byte = f2.read(1)
      if (not current_byte):
        break
      val = ord(current_byte)
      print hex(val),
  print

This program produces the output:

0xff 0xd8 0xff 0xe0 0x0 0x10 0x4a

answered Jun 13, 2017 at 21:39

slashdottir

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blueshit · Accepted Answer · 2018-01-24 10:39:18Z

0

import binascii

with open(absolutePathInput, "rb") as f:
    buff = f.read()

line = binascii.hexlify(buff)
hex_string = [line[i:i+2] for i in range(0, len(line), 2)]

simple and violent

answered Jan 24, 2018 at 10:39

blueshit

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