写一个读取文件的程序，把每一行拆分成一个个词，去掉空白和标点符号，然后把所有单词都转换成小写字母的。
Write a program that reads a file, breaks each line into words, strips whitespace and punctuation from the words, and converts them to lowercase.
例外情况，一个监听器将输入字符串转换成大写字母，而另一个将其转换成小写字母，这对于监听器所编写的代码都是完全相同的。
With the exception that one of the listeners converts the input string to uppercase, while the second converts the string to lowercase, the code for the listeners is exactly the same.
它们只是分别将字符串都转换成大写字母或小写字母。
They simply convert the string to all uppercase or all lowercase letters, respectively.
它们只是分别将字符串都转换成大写字母或小写字母。
They simply convert the string to all uppercase or all lowercase letters, respectively.
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