Write a Binary Sequence in ASCII to Binary python

Question

I'm implementing Huffman Algorithm, but when I got the final compressed code, I've got a string similar to below:

10001111010010101010101

This is a binary code to created by the paths of my tree's leafs.

I have this sequence, but when I save it in a file, all that happens is system saving it as a ASCII on a file, which I can't compress because it has the same or bigger size than the original.

How do I save this binary directly?

PS: if I use some function to convert my string to binary, all I got is my ASCII converted to binary, so I did nothing, I need a real solution.

And how many bytes is this supposed to be written as? Big endian, little endian? — Martijn Pieters
– Martijn Pieters, Commented Aug 8, 2014 at 22:05
You could use the Bitwise I/O recipe mentioned in this answer of mine to another question about reading bits. — martineau
– martineau, Commented Aug 9, 2014 at 3:19

Mark Ransom · Accepted Answer · 2014-08-08 23:06:57Z

1

What you need to do is take each 8 bits and convert it into a byte to write out, looping until you have less than 8 bits remaining. Then save whatever's left over to prepend in front of the next value.

def binarize(bitstring):
    wholebytes = len(bitstring) // 8
    chars = [chr(int(bitstring[i*8:i*8+8], 2)) for i in range(wholebytes)]
    remainder = bitstring[wholebytes*8:]
    return ''.join(chars), remainder

answered Aug 8, 2014 at 23:06

Mark Ransom

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2 Comments

alanfortlink Over a year ago

How to get back this value from the file, because your solution have worked, but I have no idea how to read it back.

Mark Ransom Over a year ago

@user3923894 that sounds like another question.

Matt Adams · Accepted Answer · 2014-08-08 22:56:31Z

0

I think you just want int() with a base value of 2:

my_string = "10001111010010101010101"
code_num = int( my_string, 2 )

Then write to a binary file. struct.pack additionally allows you to specify whatever byte order you like.

myfile = open("filename.txt",'wb')
mybytes = struct.pack( 'i', code_num )
myfile.write(mybytes)
myfile.close()

This method will also write some number of leading zeros, which could cause trouble for your Huffman codes.

edited Aug 8, 2014 at 22:56

answered Aug 8, 2014 at 22:17

Matt Adams

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2 Comments

Mark Ransom Over a year ago

Huffman codes tend to be a variable number of bits, so you can't convert to a constant size integer.

Matt Adams Over a year ago

Edited to allow larger ints

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