Set based game of life

gameoflife3.py

def candidates_for(world):
    return set.union(*[neighbours_of(cell) | set([cell]) for cell in world])

DIRECTIONS = {(-1, 1),  (0, 1),  (1,  1),
              (-1, 0),           (1,  0),
              (-1, -1), (0, -1), (1, -1)}


def neighbours_of(cell):
    x, y = cell
    return set((x+dx, y+dy) for dx, dy in DIRECTIONS)


def judge(cell, world):
    neighbour_count = len(neighbours_of(cell) & world)
    return neighbour_count in (2, 3) if cell in world else neighbour_count == 3


def evolve(world):
    return set(c for c in candidates_for(world) if judge(c, world))


def test_single_cell_dies():
    single_cell = {(0, 0)}
    assert evolve(single_cell) == set([])


def test_square_remains():
    square = {(0, 0), (0, 1), (1, 0), (1, 1)}
    assert evolve(square) == square


def test_blinker_blinks():
    blinker_1 = {(0, -1), (0, 0), (0, 1)}
    blinker_2 = {(-1, 0), (0, 0), (1, 0)}

    assert evolve(blinker_1) == blinker_2
    assert evolve(blinker_2) == blinker_1


def test_three_diagonal_cells_evolve_to_single_cell():
    assert evolve({(-1, -1), (0, 0), (1, 1)}) == {(0, 0)}


def test_three_cells_in_angle_evolves_to_square():
    angle = {(0, 0), (0, 1), (1, 0)}
    square = {(0, 0), (0, 1), (1, 0), (1, 1)}
    assert evolve(angle) == square