heuristic sudoku solution

sudokuSolution.py

def solve(grid):
    empty_cell = find_empty_cell(grid)
    if not empty_cell:
        return grid

    row, col = empty_cell
    possible_numbers = get_possible_numbers(grid, row, col)
    for num in possible_numbers:
        grid[row][col] = num
        solved_grid = solve(grid)
        if solved_grid:
            return solved_grid
        grid[row][col] = 0
    return None

def find_empty_cell(grid):
    min_possible_numbers = float("inf")
    empty_cell = None
    for row in range(9):
        for col in range(9):
            if grid[row][col] == 0:
                possible_numbers = len(get_possible_numbers(grid, row, col))
                if possible_numbers < min_possible_numbers:
                    min_possible_numbers = possible_numbers
                    empty_cell = (row, col)
    return empty_cell

def get_possible_numbers(grid, row, col):
    used_numbers = set(grid[row][i] for i in range(9)) | \
                   set(grid[i][col] for i in range(9))

    row_start = (row // 3) * 3
    col_start = (col // 3) * 3
    used_numbers |= {grid[row_start + i][col_start + j] for i in range(3) for j in range(3)}

    return [num for num in range(1, 10) if num not in used_numbers]