import re

zen='''

The Zen of Python, by Tim Peters

Beautiful is better than ugly.

Explicit is better than implicit.

Simple is better than complex.

此处略去15行...

Namespaces are one honking great idea -- let's do more of those!

'''

s=re.findall('[a-zA-Z]+',zen)

counts={}

for w in s:

    counts[w]=counts.get(w,0)+1

items=list(counts.items())

items.sort(key=lambda x:x[1],reverse=True)

for i in range(20):

    word,count=items[i]

    print("{0:<15}{1:>5}".format(word,count))

此题综合利用正则式、字典、列表、lambda等，很典型很实用，我出试卷的必考题