how to search repeated number in 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: how to check if there are duplicates in a list python

>>> your_list = ['one', 'two', 'one']
>>> len(your_list) != len(set(your_list))
True