python 统计文本文件中单词出现的个数

如题：

#!/usr/bin/env python# encoding: utf-8import rewith open('a.txt', 'r') as f:    dictResult = {}    # Find the letters each line    for line in f.readlines():        listMatch = re.findall('[a-zA-Z]+', line.lower()) # remember to lower the letters    # Count        for eachLetter in listMatch:            eachLetterCount = len(re.findall(eachLetter, line.lower()))            dictResult[eachLetter] = dictResult.get(eachLetter, 0) + eachLetterCount    # Sort the result    result = sorted(dictResult.items(), key=lambda d: d[1], reverse=True)    for each in result:        print each