I have a string of 1's and 0's in Python and I would like to write it to a binary file. I'm having a lot of trouble with finding a good way to do this.
Is there a standard way to do this that I'm simply missing?
-
2The standard way is never to traffic in strings of "1"s and "0"s. Where did these strings come from?Russell Borogove– Russell Borogove2011-10-11 21:45:28 +00:00Commented Oct 11, 2011 at 21:45
-
4There is not meaningfully such a thing as "a binary file". All files are 'binary'; they contain sequences of bits. It sounds like what you mean is "I want to interpret each '1' and '0' character in the string as a single bit, group sets of 8 bits into bytes, and write the result to file".Karl Knechtel– Karl Knechtel2011-10-11 22:08:23 +00:00Commented Oct 11, 2011 at 22:08
-
@KarlKnechtel. Sure, yes, that's what I would like to do. But I'm getting errors when I try do to that, much in the same way as liori suggested below. I've explained the problem a little below.sevandyk– sevandyk2011-10-12 01:11:14 +00:00Commented Oct 12, 2011 at 1:11
-
@RussellBorogove. I agree, it's terrible, but it's for an assignment for a course. I wish I had a choice. :)sevandyk– sevandyk2011-10-12 01:11:25 +00:00Commented Oct 12, 2011 at 1:11
Add a comment
|
5 Answers
If you want a binary file,
>>> import struct
>>> myFile=open('binaryFoo','wb')
>>> myStr='10010101110010101'
>>> x=int(myStr,2)
>>> x
76693
>>> struct.pack('i',x)
'\x95+\x01\x00'
>>> myFile.write(struct.pack('i',x))
>>> myFile.close()
>>> quit()
$ cat binaryFoo
�+$
Is this what you are looking for?
answered Oct 11, 2011 at 21:21
Lelouch Lamperouge
8,4979 gold badges51 silver badges62 bronze badges
5 Comments
Austin Marshall
The limit of possible values of myStr is pretty low ('i' format requires -2147483648 <= number <= 2147483647). You'd have to break it up into smaller values. Regardless, there's not enough information provided in the question to truly answer it.
Lelouch Lamperouge
@oxtopus, Agreed that the range is limited. But what other way would you suggest?
Karl Knechtel
@oxtopus agreed that there's not really enough information, but we all seem to be mind-reading the OP in the same way... :)
sevandyk
It's close, but myStr is really big in my case - about 100000 long. So I get a an error because "an argument is out of range." I'm able to get around that using a buffer, sorta, of length 31, but that's not quite right - my file size in the end is a little bigger than it should be. Chopping my string into substrings of length 32 gives an "argument out of range" error again. Thoughts?
Karl Knechtel
We're not psychic; you're going to have to show (perhaps in a new question) how you are "chopping your string into substrings of length 32" and processing the result.
In [1]: int('10011001',2)
Out[1]: 153
Split your input into pieces of eight bits, then apply int(_, 2) and chr, then concatenate into a string and write this string to a file.
Something like...:
your_file.write(''.join(chr(int(your_input[8*k:8*k+8], 2)) for k in xrange(len(your_input)/8)))
2 Comments
sevandyk
This is what I was trying to do, but I get a UnicodeEncodeError when I try to write the string. Apparently, this is because there is some character that is not supported by ascii in the string - but the doc for chr() says it returns only ascii characters. Thoughts?
liori
@sevandyk: is it python 3? is your string of zeros and ones actually a unicode object? do you open your file in a binary mode (
open(..., 'wb'))?There is a bitstring module now which does what you need.
from bitstring import BitArray
my_str = '001001111'
binary_file = open('file.bin', 'wb')
b = BitArray(bin=my_str)
b.tofile(binary_file)
binary_file.close()
You can test it from the shell in Linux with xxd -b file.bin
answered Jun 3, 2013 at 14:45
TheMeaningfulEngineer
16.5k28 gold badges93 silver badges148 bronze badges
1 Comment
Braden Brown
What package contains bitstring? I tried installing it, but I got the error "The following packages are not available from current channels"
Or you can use the array module like this
$ python
Python 2.7.2+ (default, Oct 4 2011, 20:06:09)
[GCC 4.6.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import random,array
#This is the best way, I could think of for coming up with an binary string of 100000
>>> binStr=''.join([str(random.randrange(0,2)) for i in range(100000)])
>>> len(binStr)
100000
>>> a = array.array("c", binStr)
#c is the type of data (character)
>>> with open("binaryFoo", "ab") as f:
... a.tofile(f)
...
#raw writing to file
>>> quit()
$
Comments
BITS_IN_BYTE = 8
chars = '00111110'
bytes = bytearray(int(chars[i:i+BITS_IN_BYTE], 2)
for i in xrange(0, len(chars), BITS_IN_BYTE))
open('filename', 'wb').write(bytes)
