Python program to return first non-repeating letter - Codewars solution.

def first_non_repeating_letter(string):

    low_str = []

    for i in string:

        low_str.append(i.lower())

    for i in string:

        if low_str.count(i.lower()) == 1:

            return i

    return ''

print(first_non_repeating_letter('sTreSS'))