Python3: Class (or static) variable definition relative to another

Question

On Ubuntu MATE 17.04 Python: 3.5

I'm sublassing a ttk Button:

import tkinter as tk
import tkinter.ttk as ttk

class ImgButton(ttk.Button):
    """
    Button for holding an image
    """
    IMG_NAME = 'filename{}.jpg'
    IMAGES_DIR = os.path.sep + os.path.sep.join(['home', 'user', 'MyProjects', 'myProject', 'resources', 'images'])
    UNKNOWN_IMG = os.path.sep.join([IMAGES_DIR, IMG_NAME.format(0)])
    IMAGES = [os.path.sep.join([IMAGES_DIR, IMG_NAME.format(i)]) for i in [1,2,3,4,5,6]]

    # ... more code... You can add an empty __init__() if you like so

if __name__ == '__main__':
    root = tk.Tk()
    ImgButton(root).pack()

When using the button it gives me an error:

NameError: name 'IMAGES_DIR' is not defined

How is it possible that UNKNOWN_IMAGE has no problem using the IMAGES_DIR variable and IMAGES raises this error???

I'm shocked with this. Do I need some static initializer? Do I need to refer to he variable in another way? In the former line it worked with nothing. And I tried ImgButton.IMAGES_DIR and it doesn't work.

How should I solve this problem? And the most important thing, what am I doing wrong?

@juanpa.arrivillaga There is no calling code needed for the error. Just defining the class gives an error. — madtyn, Oct 09 '17 at 16:29
But you're right. I thought better and I'm adding a calling code. — madtyn, Oct 09 '17 at 16:33
Aha! Yeah, I forgot, this is a common error due to the way class scope and list-comprehension scope is implemented. I'm marking this as a duplicate. I think you should just be able to use a for-loop to fix your problem. — juanpa.arrivillaga, Oct 09 '17 at 16:53

Python3: Class (or static) variable definition relative to another

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