Advent of code 2021 day 9 part 2

def countbasin(hm,i,j,cnt = 0):
    if hm[i][j] < 9:
        cnt+=1
        hm[i][j]=9
        for x,y in [(0,-1), (0,1), (-1,0), (1,0)]:
            hm,cnt = countbasin(hm,i+x,j+y,cnt)
    return hm,cnt

hm = [list(map(int,list('9'+i.replace("\n","")+'9'))) for i in open("input.txt").readlines()]
hm = [[9]*len(hm[0])] + hm + [[9]*len(hm[0])]

basins = [countbasin(hm,i,j)[1] for i in range(1,len(hm)-1) for j in range(1,len(hm[0])-1) if ((hm[i][j] < hm[i][j-1]) and (hm[i][j] < hm[i][j+1]) and (hm[i][j] < hm[i-1][j]) and (hm[i][j] < hm[i+1][j]))]

basins.sort(reverse=True)
print(basins[0]*basins[1]*basins[2])