How to read a file byte by byte in Python and how to print a bytelist as a binary?

Question

I'm trying to read a file byte by byte, but I'm not sure how to do that. I'm trying to do it like that:

file = open(filename, 'rb')
while 1:
   byte = file.read(8)
   # Do something...

So does that make the variable byte to contain 8 next bits at the beginning of every loop? It doesn't matter what those bytes really are. The only thing that matters is that I need to read a file in 8-bit stacks.

EDIT:

Also I collect those bytes in a list and I would like to print them so that they don't print out as ASCII characters, but as raw bytes i.e. when I print that bytelist it gives the result as

['10010101', '00011100', .... ]

This question is very similar to http://stackoverflow.com/questions/1035340/reading-binary-file-in-python. — Randall Cook, Feb 01 '13 at 07:12
@Wilson It is generally better to use purely truthy or falsy values. Even though `while 1` and `while True` achieve the same result, `while True` is a lot more descriptive and readable. — zaplec, May 05 '20 at 16:19

score 40 · Answer 1 · answered May 20 '10 at 09:16

40

To read one byte:

file.read(1)

8 bits is one byte.

answered May 20 '10 at 09:16

Mark Byers

767,688
176
1,542
1,434

1

Thanks. I thought that file.read(1) would read just one bit, but seems it reads one byte. – zaplec May 20 '10 at 09:25
You can use file.seek(3) to move the file pointer to the 3rd character – Christian Vorhemus Jun 01 '19 at 18:05

score 19 · Accepted Answer · answered May 20 '10 at 14:37

To answer the second part of your question, to convert to binary you can use a format string and the ord function:

>>> byte = 'a'
>>> '{0:08b}'.format(ord(byte))
'01100001'

Note that the format pads with the right number of leading zeros, which seems to be your requirement. This method needs Python 2.6 or later.

score 17 · Answer 3 · answered May 20 '10 at 09:17

17

The code you've shown will read 8 bytes. You could use

with open(filename, 'rb') as f:
   while 1:
      byte_s = f.read(1)
      if not byte_s:
         break
      byte = byte_s[0]
      ...

answered May 20 '10 at 09:17

kennytm

491,404
99
1,053
989

score 2 · Answer 4 · answered Aug 24 '11 at 12:00

2

There's a python module especially made for reading and writing to and from binary encoded data called 'struct'. Since versions of Python under 2.6 doesn't support str.format, a custom method needs to be used to create binary formatted strings.

import struct

# binary string
def bstr(n): # n in range 0-255
    return ''.join([str(n >> x & 1) for x in (7,6,5,4,3,2,1,0)])

# read file into an array of binary formatted strings.
def read_binary(path):
    f = open(path,'rb')
    binlist = []
    while True:
        bin = struct.unpack('B',f.read(1))[0] # B stands for unsigned char (8 bits)
        if not bin:
            break
        strBin = bstr(bin)
        binlist.append(strBin)
    return binlist

answered Aug 24 '11 at 12:00

Owen Champion

21
2

1

If you're just using it for a single character, surely you'd do better to just use `ord(f.read(1))` instead of `struct.unpack('B', f.read(1))[0]`? (You'd need to make it something like `c = f.read(1); if not c: break; binlist.append(bstr(ord(c)))`.) – Chris Morgan Dec 13 '11 at 09:52
I've got this error: ---> 12 bin = struct.unpack('B',f.read(1))[0] # B stands for unsigned char (8 bits) error: unpack requires a buffer of 1 bytes – MGM Oct 31 '18 at 12:14

score 0 · Answer 5 · answered May 26 '14 at 12:11

Late to the party, but this may help anyone looking for a quick solution:

you can use bin(ord('b')).replace('b', '')bin() it gives you the binary representation with a 'b' after the last bit, you have to remove it. Also ord() gives you the ASCII number to the char or 8-bit/1 Byte coded character.

Cheers

How to read a file byte by byte in Python and how to print a bytelist as a binary?

5 Answers5

Linked