如何使用字符串格式迭代嵌套字典？

def iterate_nested_dict(nested_dict, prefix=''):
    for key, value in nested_dict.items():
        if isinstance(value, dict):
            iterate_nested_dict(value, prefix + key + '.')
        else:
            print(prefix + key + ': ' + str(value))

# 示例嵌套字典
nested_dict = {
    'name': 'John',
    'age': 30,
    'address': {
        'street': '123 Main St',
        'city': 'New York',
        'country': 'USA'
    }
}

iterate_nested_dict(nested_dict)

name: John
age: 30
address.street: 123 Main St
address.city: New York
address.country: USA