function to find the non repeating character in a string

non_repeating_character_dict_method.py

#@time_it
def dict_method(st):
    '''
    This function will return the non-repeating
    characters in a string 
    
    Args:
        st: the input string
    
    Return:
        unique: a list of characters that don't
                repeat in the string
    '''
    d = {}
    for letter in st:
        if letter not in d :
            d[letter] = 1
        else:
            d[letter] += 1
            
    unique = [k for k,v in d.items() if v==1]
    return unique