Write a program that reads a file, breaks each line into words, scripts whitespace and punctuation from the words, and converts them to lowercase. Modify the program to print the 20 most frequently-used words in the book.
First I downloaded the e-book ‘ELSIE‘S WINTER TRIP’ in the below dictionary:
Scripts:
from Thinking in Python
Word frequency analysis,布布扣,bubuko.com
原文：http://www.cnblogs.com/ryansunyu/p/3903443.html