FirstNonRepeatingLetter.py

# Write a function named first_non_repeating_letter that takes a string input, and returns the first character that is not repeated anywhere in the string.

# For example, if given the input 'stress', the function should return 't', since the letter t only occurs once in the string, and occurs first in the string.

# As an added challenge, upper- and lowercase letters are considered the same character, but the function should return the correct case for the initial letter. For example, the input 'sTreSS' should return 'T'.

# If a string contains all repeating characters, it should return an empty string ("") or None -- see sample tests.


def first_non_repeating_letter(s):
    for letter in s:
        if s.lower().count(letter.lower()) == 1:
            return letter
    return ''


# fairly simple, we just use count and a for loop to match the count of the lower() of our s to =1 or return ''