def mnum(xli):
    d = defaultdict(int)
    for ch in xli:
        d[ch] += 1
    x=[i for i in d.values()]
    # ①
    # print(list(d.keys())[list(d.values()).index(max(x))])
    # ②
    z=[i for i,j in d.items() if j==max(x)]
    return z
x=[48,7,9,4,5,1,8,75,74,5,1]
print(mnum(x))

A. 充分利用 keys() 、values()、index() 函数

>>> list (student.keys()) [list (student.values()).index ('1004')]

#-----------------------------------------------------------------------------------

B. 通过定义get_key函数的方式

>>> def get_key (dict, value):

               return [k for k, v in dict.items() if v == value]

>>> get_key (student, '1002')'

#-----------------------------------------------------------------------------------

C. 将原字典dict进行反转得新字典new_dict，由原来的K-V存储形式，变为V-K存储形式

>>> new_dict = {v : k for k, v in dict.items()}

>>> new_dict ['1001']