repeating no in a list python code example

Example 1: duplicate in list python

a = [1,2,3,2,1,5,6,5,5,5]

import collections
print([item for item, count in collections.Counter(a).items() if count > 1])

## [1, 2, 5]

Example 2: sort and remove duplicates list python

myList = sorted(set(myList))