python之将新字典添加到现有字典中作为键的值

我有一本字典:

my_dict = { 
    "apples":"21", 
    "vegetables":"30", 
    "sesame":"45", 
    "papaya":"18", 
} 

我想生成一个新的，如下所示:

my_dict = { 
    "apples" : {"apples":"21"}, 
    "vegetables" : {"vegetables":"30"}, 
    "sesame" : {"sesame":"45"}, 
    "papaya" : {"papaya":"18"}, 
} 

我写了这样一段代码....

my_dict = { 
    "apples":"21", 
    "vegetables":"30", 
    "sesame":"45", 
    "papaya":"18", 
} 
 
new_dict={} 
new_value_for_dict={} 
 
for key in my_dict: 
    new_value_for_dict[key]= my_dict[key] 
    new_dict[key]= new_value_for_dict 
    # need to clear the last key,value of the "new_value_for_dict" 
 
print(new_dict) 

输出如下:

{'vegitables':{'vegitables': '30', 'saseme': '45',  
               'apples': '21','papaya': '18'}, 
 'saseme':{'vegitables': '30', 'saseme': '45',  
           'apples': '21', 'papaya': '18'},  
 'apples': {'vegitables': '30', 'saseme': '45',  
            'apples': '21', 'papaya': '18'},  
 'papaya': {'vegitables': '30', 'saseme': '45',  
            'apples': '21', 'papaya': '18'} 
} 

但不是我所期望的那样。如何消除重复？ 我该如何纠正它？