Number of Islands question recursive DFS solution

number_of_islands_dfs.py

class Solution:
    def numIslands(self, grid):
        # They have empty input
        if not grid:
            return 0
        directions = {"up": (-1,0), "down":(1,0), "left":(0,-1), "right":(0,1)}
        island_number = 0
        lenx, leny =  len(grid), len(grid[0])
        
        def land_zeroizer(x, y):
            # stop if out of bounds
            if x<0 or y<0 or x>=lenx or y>=leny:
                return
            # stop if reached to the sea
            if grid[x][y] == '0':
                return
            
            # Make every visited land into sea
            grid[x][y] = '0'
            
            # Go to each direction
            for way in directions:
                i,j = directions.get(way)
                land_zeroizer(x+i,y+j)
        
        # Check each tile
        for i, row in enumerate(grid):
            for j, land in enumerate(row):
                if land == '0':
                    continue
                # If it is a land, then we make everything connected to it into sea and increase island number by 1
                land_zeroizer(i,j)
                island_number +=1
        
        return island_number