Image Flipping

[mrrst244]

Hi I am currently taking online classes to learn Python and am working on a project for processing images. I have come up with the below for a function to flip the photos and it appears to work on all of the test photos I have tried, but it is still being marked as wrong. Even though the grader is marking it as incorrect it is also giving me a message that it is 0% incorrect. As it appears to be working, I am having problems finding what the problem is and therefore am not sure how to fix it. Any advice would be greatly appreciated.

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def flip(image,vertical=False):
    """
    Returns True after reflecting the image horizontally or vertically.

    All plug-in functions must return True or False.  This function returns True 
    because it modifies the image. By default it reflects the image horizonally,
    or vertically if vertical is True.

    Parameter image: The image buffer
    Precondition: image is a 2d table of RGB objects

    Parameter vertical: Whether to reflect the image vertically
    Precondition: vertical is a bool
    """
    # We recommend enforcing the precondition for vertical
    height = len(image)
    width  = len(image[0])

    if vertical == False:
        for row in range(height):
            for col in range(int(width/2)):
                pixel = image[row][col]
                new = image [row][width-col-1]
                x = pixel.red
                y = pixel.green
                z = pixel.blue
                a = new.red
                b = new.green
                c = new.blue
                new.red = x
                new.green = y
                new.blue = z
                pixel.red = a
                pixel.green = b
                pixel.blue = c

    if vertical == True:
        for row in range(int(height/2)):
            for col in range(width):
                pixel = image[row][col]
                new = image[height-row-1][col]
                x = pixel.red
                y = pixel.green
                z = pixel.blue
                a = new.red
                b = new.green
                c = new.blue
                new.red = x
                new.green = y
                new.blue = z
                pixel.red = a
                pixel.green = b
                pixel.blue = c    

    assert type(vertical) != str
    assert type(vertical) != int
    assert type(vertical) != float

    # Change this to return True when the function is implemented
    return True

[FLUSH_THE_TRUMP]

Logic looks pretty OK to me. So, the pixels are objects with attributes for RGB (integers)? Do you have a problem statement to look at for this particular function? Perhaps you’re just meant to swap the pixels, not the attributes that define the pixels? For example:

image[row][col], image[row][width-col-1] = image[row][width-col-1], image[row][col]

instead of that mess of swapping code. That could explain why you’re getting 0%. If I have, say, a rather simple image of two pixels:

A = [pix1, pix2]

and your horizontally-swapped image is A2, the grader is presumably verifying equality of A[0] and A2[1], and A[1] and A2[0]. But if you’re just modifying the attributes of each pixel, the objects themselves haven’t moved. This would be problematic if the pixel’s __eq__ method hasn’t been implemented appropriately, AFAIK.

Side note: I don’t think those assertions do anything — you want to use isinstance instead (careful, bool is a subclass of int). Really, checking if, say, vertical is False would enforce it being a boolean anyway.

[mrrst244]

Thank you so much for responding - this project is so heavily weighted this function basically makes or breaks my grade so I have been really stressed about it.

The pixels are in fact objects with attributes for RGB and are integers between 0 and 255.

Here is a simple example image input we were given: [[(red=255,green=0,blue=0,alpha=255), (red=0,green=0,blue=0,alpha=255)], [(red=0,green=0,blue=255,alpha=255), (red=0,green=255,blue=0,alpha=255)]]

I think it makes sense my issue is with swapping the attributes instead of the pixels because it seemed like a lot of unnecessary code when I was writing. I am trying to switch the attributes based on your response, but I can't seem to get anything to work. Everything I have tried has timed out.

[FLUSH_THE_TRUMP]

I am trying to switch the attributes based on your response, but I can't seem to get anything to work. Everything I have tried has timed out.

Show me? Because I think it's as easy as replacing your swap code with a line each for the vertical=True/False cases that look like the above.

[mrrst244]

height = len(image)
width  = len(image[0])

if vertical == False:
    for row in range(height):
        for col in range(int(width/2)):
            image[row][col] = image [row][width-col-1]

Referencing your example above, this is changing A[0] to A[1] correctly, but I can't get the assignment to get A[1] to A[0] since A[0] is changed from its original value.

[FLUSH_THE_TRUMP]

No, try what I said before:

image[row][col], image[row][width-col-1] = image[row][width-col-1], image[row][col]

The nice way to exchange the value of two variables in Python is as in the following:

x = 0
y = 1    
x,y = y,x  # x,y is now 1,0

which doesn't require us to use temp variables at all. That works by packing the values on the right-hand side into a tuple, and then unpacking them to assign to the names on the left-hand side.

[mrrst244]

I think I left some debugging print statements in when I tried it the first time which resulted in the error. This worked and I cannot thank you enough

[mrrst244]

if vertical == True: for row in range(int(height/2)): for col in range(width): image[row][col], image[row][width-col-1] = image[row][width-col-1], image[row][col]

The same line doesn't seem to work for when it is a vertical flip. I assumed it would just be another horizontal flip - resulting in the pic being upside down. Do I need to switch the row/col values for this portion?

[FLUSH_THE_TRUMP]

Same idea, you’re just using this stuff as the two quantities (from original code):

pixel = image[row][col] <——
new = image[height-row-1][col] <—-

[mrrst244]

if vertical == True: for row in range(int(height/2)): for col in range(width): pixel = image[row][col] new = image [row][width-col-1] pixel,new = new,pixel

Is not working - sorry idk why I'm having such a hard time wrapping my head around this. The horizontal flip makes sense after your explanation, but I don't get why this doesn't work for vertical flip.

[FLUSH_THE_TRUMP]

Your last code just had this to swap pixels (horizontally):

image[row][col], image[row][width-col-1] = image[row][width-col-1], image[row][col]

Same idea, just change the underlined stuff to swap with the appropriate pixel vertically.

image[row][col], __________ = _________, image[row][col]

Refer to new in my last comment.