Question

This is being implemented with Python and Pygame but it’s a fairly general programming question (meaning implementation independent).

I have a function which takes as input an x and y integer and should generate a 3×3 grid of neighbouring points (the x and y included).

Note: the 0,0 origin begins at the top left. x increases as you move right, y increases as you move down.

Eg.

def nearest_grid(x, y):
    return [[(x-1,y-1),(x,y-1),(x+1,y-1)],[(x-1,y)(x,y),(x+1,y)],[(x-1,y+1),(x,y+1),(x+1,y+1)]]

So, given a grid and a point (marked p) it returns the following as a list of 3 lists:

x  x  x
x  p  x
x  x  x

Is this the most effective / legible way to do this in Python?

EDIT: Suppose I wanted to pass a radius value (where the above radius value would be 1). So, if I passed a radius value of 2 then the above method would quickly become tiresome. Is there a more general way?

Answer 1

def nearby_grid_points(x, y, r=1):
    res = []
    for dy in xrange(-r, r+1):
        res.append([(x+dx, y+dy) for dx in xrange(-r, r+1)])
    return res