def words_before_word(list,word):
    sum=0
    i=0
    while i<len(list) and list[i]!=word:
        if type(list[i])==type("aa"):
            sum+=1
        i+=1
    if sum==len(list):
        return None

    return sum
print(words_before_word(["tt","aaaaa","aaaaa"],"sam"))