对嵌套字典中的值求和

nested_dict = {
    'a': {
        'x': 1,
        'y': 2,
        'z': 3
    },
    'b': {
        'x': 4,
        'y': 5,
        'z': 6
    },
    'c': {
        'x': 7,
        'y': 8,
        'z': 9
    }
}

def sum_nested_dict(nested_dict):
    total_sum = 0
    for value in nested_dict.values():
        if isinstance(value, dict):
            total_sum += sum_nested_dict(value)
        else:
            total_sum += value
    return total_sum

result = sum_nested_dict(nested_dict)
print(result)  # 输出：45