duplicate in list python

1some_list=['a','b','c','b','d','m','n','n']
2
3 my_list=sorted(some_list)
4 
5duplicates=[]
6for i in my_list:
7     if my_list.count(i)>1:
8         if i not in duplicates:
9             duplicates.append(i)
10 
11print(duplicates)

1a = [1,2,3,2,1,5,6,5,5,5]
2
3import collections
4print([item for item, count in collections.Counter(a).items() if count > 1])
5
6## [1, 2, 5]

1def Find_Repeated(x):
2    x2=sorted(x)
3    List_Of_Repeated=[]
4    for i in x2:
5        if x2.count(i)>1:
6            List_Of_Repeated.append([i,x2.count(i)])
7            for c in range(x2.count(i)):
8                for j in x2:
9                    if i==j and x2.count(i)>1:
10                        x2.remove(i)
11    List_Of_Repeated.sort()
12    return List_Of_Repeated
13
14List=[1,2,3,4,4,4,5,5,5,5,5,1,1,2,2,3,7,8,6]
15
16# Repeated numbers: [1,2,3,4,5]
17
18# Simple print output:
19
20print(Find_Repeated(List),"\n")
21
22# For a neat output:
23
24print("[ Value , Times Repeated ] \n")
25print("For example: [2,4]  The value 2 was repeated 4 times. \n")
26for i in Find_Repeated(List):
27    print(i)
28