def get_pixel_at(pixel_grid, i, j):
    '''
    Returns the pixel in pixel_grid at row i and column j (zero-indexed).
    Returns 0 if i or j is out of bounds for the given pixel_grid.
    '''
    if i>=0 and j>=0: 
    	if i<len(pixel_grid) and j<len(pixel_grid[i]):
        	return pixel_grid[i][j]
        else: 
        	return 0
    else:
        return 0
 
def average_of_surrounding(pixel_grid, i, j):
    '''
    Returns the unweighted average of the values of the pixel at row i 
    and column j and the eight pixels surrounding it.
    '''
    pixel_sum = 0
    for r in [i-1, i, i+1]:
        for c in [j-1, j, j+1]:
            pixel_sum=pixel_sum+get_pixel_at(pixel_grid, r, c)
    # pixel_sum should be an integer. We intend for this to be 
    # truncating integer division.  
    return pixel_sum / 9
 
def blur(pixel_grid):
    '''
    Given pixel_grid (a grid of pixels), returns a new grid of pixels
    that is the result of blurring pixel_grid. In the output grid, 
    each pixel is the average of that pixel and its eight neighbors in
    the input grid. 
    '''
 
    new_grid=pixel_grid
    for r in range(0, len(pixel_grid)):
        for c in range(0, len(pixel_grid[r])):
            new_grid[r][c]=average_of_surrounding(pixel_grid, r, c)
    return new_grid
 
def test_average_of_surrounding():
    test_grid = [
        [1, 2, 3],
        [4, 5, 6],
        [7, 8, 9]
    ]
 
    print blur(test_grid)
test_average_of_surrounding()

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