to find recurring element in a list 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: program to print duplicates from a list of integers in python

lst = [ 3, 6, 9, 12, 3, 30, 15, 9, 45, 36, 12, 12]
dupItems = []
uniqItems = {}
for x in lst:
   if x not in uniqItems:
      uniqItems[x] = 1
   else:
      if uniqItems[x] == 1:
         dupItems.append(x)
      uniqItems[x] += 1
print(dupItems)