save a sequence of bits into a binary file (not in 8-bit format)

Question

I have a sequence of bits for example 0101, and I want to save this sequence to a file in binary format and while opening the saved file using a binary viewer, I need to show me exactly 0101 [I mean 4 bits]. but it showed me 00000000 00000001 00000000 00000001 [and this is 32 bits]. May I ask you to help me guys? Thanks

My Code:

f = open('my_file', 'w+b')
byte_arr = [0, 1, 0, 1]
binary_format = bytearray(byte_arr)
print(binary_format)
f.write(binary_format)
f.close()

The Screenshot:

Binary viewers are always going to show groups of 8 bits, that's just the way they work. — Mark Ransom
– Mark Ransom, Commented Jul 29, 2021 at 17:47
@MarkRansom Thank for you reply. You mean I can not save 0101 in a file? — Aaron
– Aaron, Commented Jul 29, 2021 at 17:49
There is no way to write only 4 bits to a file. If you try, you'll get 8 bits anyway. — Mark Ransom
– Mark Ransom, Commented Jul 29, 2021 at 17:51
You might find the answers to How to read bits from a file? useful (esp my own which also features a BitWriter class). — martineau
– martineau, Commented Jul 29, 2021 at 18:30

Cory Kramer · Accepted Answer · 2021-07-29 17:45:10Z

0

If you want to bit sequence 0101 then you can define that using a binary literal

>>> 0b0101
5  # in decimal

If you are starting from an array of bits, then you can use int with base 2

>>> byte_arr = [0, 1, 0, 1]
>>> int(''.join(str(i) for i in byte_arr), 2)
5

answered Jul 29, 2021 at 17:45

Cory Kramer

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2 Comments

Aaron Over a year ago

Thanks for you reply. I'm working on a compression algorithm (Huffman Coding) and I want to save 0101 in a file and while right clicking on the file and go to properties, it shows me the size of 4 bits. Is it possible?

Cory Kramer Over a year ago

You cannot have a file size of only 4 bits for various reasons.

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