How to output once each character in a string?

Question

Python

this code example displays only those characters that occur once in a string

my_str = "aaaaaaaaaaaaaaaaaaaaaannnnaaaaaaaaaaaahaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaa"
for letter in my_str:
  if my_str.count(letter) == 1:
      print(letter)

response received:
h
b

--------------------------------

How to receive response:
a
n
b
h

Answer 1

print(set(my_str))

Answer 2

In [28]: s = "abac"
In [29]: for e in set(s):
    ...:     print(e)
    ...:
a
c
b