Sudoku Creator - 7s Checker

import random

def print_grid(grid):
    for row in grid:
        print(" ".join(str(num) for num in row))

def is_valid(grid, row, col, num):
    for i in range(9):
        if grid[row][i] == num or grid[i][col] == num:
            return False
    start_row, start_col = 3 * (row // 3), 3 * (col // 3)
    for i in range(start_row, start_row + 3):
        for j in range(start_col, start_col + 3):
            if grid[i][j] == num:
                return False
    return True

def fill_grid(grid):
    for row in range(9):
        for col in range(9):
            if grid[row][col] == 0:
                random_nums = list(range(1, 10))
                random.shuffle(random_nums)
                for num in random_nums:
                    if is_valid(grid, row, col, num):
                        grid[row][col] = num
                        if fill_grid(grid):
                            return True
                        grid[row][col] = 0
                return False
    return True

def generate_sudoku():
    grid = [[0] * 9 for _ in range(9)]
    fill_grid(grid)
    return grid

def check_for_sevens(grid, num_samples=30):
    flat_grid = [num for row in grid for num in row]
    selected_tiles = random.sample(flat_grid, num_samples)
    has_seven = 7 in selected_tiles
    return has_seven

# Generate a completed Sudoku grid
sudoku_grid = generate_sudoku()

# Print the Sudoku grid
print("Generated Sudoku Grid:")
print_grid(sudoku_grid)

# Run 1,000,000 trials to check for 7s
num_trials = 1000000
count_no_sevens = 0

for _ in range(num_trials):
    if not check_for_sevens(sudoku_grid):
        count_no_sevens += 1

# Calculate percentage of no-7s
percentage_no_sevens = (count_no_sevens / num_trials) * 100

# Output results
print(f"Total occurrences of no 7s: {count_no_sevens}")
print(f"Percentage of trials with no 7s: {percentage_no_sevens:.4f}%")
input()