In Python, how do you convert 8-bit binary numbers into their ASCII characters?

Question

I'm attempting to extract a hidden message from the blue pixels of a picture such that the if the blue value is even, it represents a 0 in the binary string, and if the blue value is odd, it represents a 1 in the binary string. The 8-bit binary strings each represent a character, and together, the characters become a hidden message.

I've broken up the whole binary string into 8-bit binary substrings, but how should I go about converting those "chunks" into ASCII characters? chr() and ord() and unichr() don't seem to be working. Is there a method or function that can be used to directly convert the 8-bit binary substring into its corresponding ASCII character, or do I have to go about manually converting the string?

import Image

def chunks(s, n):
    for start in range(0, len(s), n):
        yield s[start:start+n]

image = Image.open('image.png')
imagePixels = image.load()
imageWidth = image.size[0]
imageHeight = image.size[1]
blueValueEightString = "" 

for y in range(imageHeight):
    for x in range(imageWidth):
        blueValue = imagePixels[x, y][2]

        if blueValue%2 == 0:
            blueValue = 0
        else: 
            blueValue = 1

        blueValueString = str(blueValue)
        blueValueEightString += blueValueString

for chunk in chunks(blueValueEightString, 8):
    print chunk

Solution

You need to first convert it to an integer, and then you can use chr() to get the ascii character coresponding to the value:

>>> binary_string = '01110111'
>>> int(binary_string, 2)
119
>>> chr(int(binary_string, 2))
'w'

Comments

[tchrist]

You cannot convert 8-bit numbers into ASCII: you can only convert 7-bit numbers. ASCII does not hold 8 bits.

[Karl Knechtel]

It would be much better to use arithmetic to convert the data from imagePixels into numbers ranging from 0-255 directly, rather than creating strings, joining them together and converting back into a number.

[Jarad]

I've seen the use of int with a base of 2 in several examples now. Why does it make sense to use a base of 2?