Sudoku solver python

sudokuSolver.py

import numpy as np

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

print(np.matrix(grid))

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))
  input('More?')

solve()