find duplicate letters in python code example

Example 1: python find first duplicate numbers

def findDuplicateNumbers(a):
  mySet = set()
    for el in a:
        if el in mySet:
            return el
        mySet.add(el)
    return -1

Example 2: check for double character in a string python

count = {}
for s in check_string:
  if s in count:
    count[s] += 1
  else:
    count[s] = 1

for key in count:
  if count[key] > 1:
    print key, count[key]