Pythonic? That would be a simple implementation of an inverse function, using list comprehensions. We will need to count down from the max value, since Python counts backwards (if we are considering the cartegean plane).
print [[grid[y][l-x] for y in range(h)] for x in range(w)]
Where
w is the width,
h is the height, and
l =
w-1 (defined for efficiency purposes).