统计如下字符串str 中每个单词出现的次数，结果存入 dict 中，单词为key，次数为 value，
并按照 value 由高到底排序，输出此 dict
str = """The Zen of Python, by Tim Peters Beautiful is better thanugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparseisbetterthandense. Readability counts. Specialcasesaren'tspecialenoughtobreaktherules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. Thereshouldbeone--andpreferablyonlyone --obviouswayto do it. Although that way may not be obvious at first unless you're Dutch. Now is better than never. Although never is often better than *right* now. If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea. Namespacesareonehonkinggreatidea--let'sdomoreofthose!"""