Python Sudoku Solver

import numpy as np

grid = [[0,0,0,0,0,7,0,8,0],
        [4,0,8,0,0,0,0,9,0],
        [0,7,0,0,0,0,0,2,1],
        [2,0,4,3,0,5,0,0,0],
        [0,0,0,6,0,4,0,0,0],
        [0,0,0,1,0,0,3,0,2],
        [0,3,1,2,0,0,0,0,0],
        [0,0,0,0,0,0,5,0,0],
        [9,0,0,4,6,0,0,0,0]]

def possible(y,x,n) :
    global grid
    for i in range(0,9) :
        if grid[y][i] == n :
            return False
    for i in range(0,9) :
        if grid[i][x] == n :
            return False
    x0 = (x//3)*3
    y0 = (y//3)*3
    for i in range(0,3) :
        for j in range(0,3) :
            if grid[y0+i][x0+j] == n :
                return False
    return True

def solve() :
    global grid
    for y in range(9) :
        for x in range(9) :
            if grid[y][x] == 0 :
                for n in range(1,10) :
                    if possible(y,x,n) :
                        grid[y][x] = n
                        solve()
                        grid[y][x] = 0
                return
    print(np.matrix(grid))
    return