找到第一个不重复的字符

def searchOnce(s):
    if len(s)==0:
        return -1
    elif len(s)==1:
        return s[0]
    else:
        sDic={}
        once=1
        notonce=2
        for word in s:
            if not sDic.get(word):
                sDic[word]=once
            else:
                sDic[word]=notonce
        for word in s:
            if sDic[word]==once:
                return word
        return -1

if __name__ == "__main__":
    s=‘teeth‘
    print searchOnce(s)