Unused variables and TypeError: cannot unpack non-iterable int object

Question

Hello I'm a newbie at python. In my function, I keep getting warnings of unused variables r,g,b,a. Can someone explain it for me?

def encode_image(self,img, msg):
        length = len(msg)
        if length > 255:
            print("text too long! (don't exeed 255 characters)")
            return False
        encoded = img.copy()
        width, height = img.size
        index = 0
        for row in range(height):
            for col in range(width):
                if img.mode != 'RGB':
                    r, g, b ,a = img.getpixel((col, row))
                elif img.mode == 'RGB':
                    r, g, b = img.getpixel((col, row))
                # first value is length of msg
                if row == 0 and col == 0 and index < length:
                    asc = length
                elif index <= length:
                    c = msg[index -1]
                    asc = ord(c)
                else:
                    asc = b
                encoded.putpixel((col, row), (r, g , asc))
                index += 1
        return encoded

Unused variable 'a' pylint(unused-variable)
Unused variable 'r' pylint(unused-variable)
Unused variable 'g' pylint(unused-variable)
Unused variable 'b' pylint(unused-variable)

   r, g, b ,a = img.getpixel((col, row))
TypeError: cannot unpack non-iterable int object

tksm! what about the unused variables? Should I care about it? — Nam Hoang
– Nam Hoang, Commented Jan 16, 2021 at 22:03
That's just a lint warning as others have said. You don't use the variables after defining them, so you don't need to define them at all — effprime
– effprime, Commented Jan 16, 2021 at 22:29

Nitish · Accepted Answer · 2021-01-16 21:57:16Z

1

Your check if img.mode !='RGB' is not sufficient. Seems like your image is greyscale, hence getpixel() will only return one integer value, hence it cannot split an integer into 4 variables. (i.e. can't unpack to 4 variables)

Use img.getbands() to find how many bands are there and then unpack accordingly.

answered Jan 16, 2021 at 21:57

Nitish

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2 Comments

Nam Hoang Over a year ago

Hello it seems like it work with RGB image and not with P-mode, meaning white-ish picture results in this error. But I still don't understand the unused variables warnings, should I do anything about it?

Nitish Over a year ago

Pylint is a code checker, it tells you the unused variables in your code, hence saving system resources. You can ignore this for now. Its useful for large projects where every byte counts.

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