Codewars: Plants and Zombies

# Zombie class
class Zombie:
    def __init__(self, health):
        self.health = health

    def remove_health(self, amount):
        if amount < self.health:
            self.health -= amount
            return 0
        else:
            rest = amount - self.health
            self.health = 0
            return rest

# Shooter class
class Shooter:
    def __init__(self, kind):
        self.kind = "N" if kind.isnumeric() else "S"
        self.shots = int(kind) if kind.isnumeric() else 1

# helper function to draw the grid
def draw_grid(grid):
    for row in grid:
        line = ""
        for item in row:
            if isinstance(item, Shooter):
                line += item.kind + " "
            elif isinstance(item, Zombie):
                line += str(item.health) + ("" if item.health > 9 else " ")
            else:
                line += ". "
        print(line)
    print("--------------")
    print()

# main game function
def plants_and_zombies(lawn, zombies):
    grid = []
    row_len = len(lawn[0]) - 1
    running = True
    move = 0

    # Place the Shooter-Objects in the Grid
    for row in range(len(lawn)):
        new_row = []
        for c in lawn[row]:
            if c == ' ':
                new_row.append(0)
            else:
                new_row.append(Shooter(c))
        grid.append(new_row)

    while running:  # main game loop

        # Move Zombies
        for i, row in enumerate(grid):
            for j, item in enumerate(row):
                if isinstance(item, Zombie):
                    grid[i][j - 1] = item
                    grid[i][j] = 0

        # Spawn Zombies
        for i, row, hp in zombies:
            if i == move:
                grid[row][row_len] = Zombie(hp)

        # The number shooters shoot in a acluster for every row
        for r, row in enumerate(grid):
            shots_in_row = 0
            for item in row:
                if isinstance(item, Shooter):
                    if item.kind == "N":
                        shots_in_row += item.shots
            for c, item in enumerate(row):
                if isinstance(item, Zombie):
                    rest = item.remove_health(shots_in_row)
                    if item.health <= 0:
                        grid[r][c] = 0
                    if rest > 0:
                        shots_in_row = rest
                    else:
                        break

        # The super shooters shoot from rigth to left and top to bottom
        for col in range(len(grid[0]) - 1, -1, -1):
            for row in range(len(grid)):
                if isinstance(grid[row][col], Shooter):
                    if grid[row][col].kind == "S":
                        for dr, dc in [(1, 1), (-1, 1), (0, 1)]:
                            if row + dr > len(grid) or row + dr < 0 or col + dc > len(grid[0]):
                                continue
                            nrow, ncol = row + dr, col + dc
                            while nrow >= 0 and nrow < len(grid) and ncol < len(grid[0]):
                                if isinstance(grid[nrow][ncol], Zombie):
                                    grid[nrow][ncol].remove_health(1)
                                    if grid[nrow][ncol].health <= 0:
                                        grid[nrow][ncol] = 0
                                    break
                                nrow += dr
                                ncol += dc

        # increase the move counter an check if the game is over
        # draw_grid(grid) helper function
        move += 1
        zombie_count = 0
        for row in grid:
            for item in row:
                if isinstance(item, Zombie):
                    zombie_count += 1
        if zombie_count <= 0:
            print("None")
            return None
        for i in range(len(grid)):
            if isinstance(grid[i][0], Zombie):
                print(move)
                return move