Pythonで文章に出現する個々のキーワードの出現回数を調べる方法

def version1(line):
    for word in line.split():
        if word in wordcount:
            wordcount[word] = wordcount[word] + 1
        else:
            wordcount[word] = 1
    print wordcount

def version2(line):
    for word in line.split():
        wordcount[word] = wordcount.get(word, 0) + 1
    print wordcount

def version3(line):
    import nltk
    tokens = nltk.word_tokenize(line)
    text = nltk.Text(tokens)
    wordcount = nltk.FreqDist(text)
    print wordcount.items()

if __name__ == '__main__':
    line = "These changes, almost all of which the White House and Democrats have said they oppose, would combine with January's tax increases to eliminate the government's budget deficit in 2023, a top GOP goal, says Mr. Ryan, chairman of the House Budget Committee. Prior House GOP budget resolutions called for changes that would have taken several decades to eliminate the deficit."
    wordcount = {}
    version1(line)
    version2(line)
    version3(line)

    print wordcount.items()[:10]