Find the first non-repeated character in a string

Question

I read of a job interview question to write some code for the following:

Write an efficient function to find the first nonrepeated character in a st

Answer 1

Python; O(N+N) I think.

def find_first_non_occuring(test_str):
    results = {}
    for letter in test_str:
        if letter in results.keys():
            if results[letter] == 1:
                results[letter] = results[letter]+1
        else:
            results[letter] = 1 

    for letter in test_str:
        if results[letter] is 1:
            return letter
test_str = 'afixuboshafe fafd weagdgdg'
print find_first_non_occuring(test_str)