def replaceWord(sentence,word):
    words = sentence.split()
    for i in range(len(words)):
        if word == words[i]:
            words[i] = "".join(['-' for _ in range(len(word))])
            break
    return " ".join(words)

def replaceMultiWords(sentence,words):
    new_str = sentence
    for i in words.split():
        new_str = replaceWord(new_str,i)
    return new_str

x = "I fucking love to eat some motherfucking dope ass pizza"

print replaceMultiWords(x,'fucking dope ass motherfucking')