我的函数返回一个空列表，但我不明白为什么？

Question

我正在编写一个带有两个参数的文件重叠函数：longestFile和shortFile。我想看看两个文件是否具有相同的编号，如果相同，它将把该编号附加到一个空列表中。 这是我用于程序的两个列表： The first file that I am using to compare和The second file that I use

def longestFile(firstFile, secondFile):
    if len(firstFile)>len(secondFile):
       return firstFile
    else:
       return secondFile

def shortestFile(firstFile, secondFile):
    if len (firstFile) < len(secondFile):
       return firstFile
    else:
       return secondFile

def middleNumber(theLongestFile):
    return theLongestFile[len(theLongestFile)//2]

def fileOverlap(lstFirstFile,lstSecondFile):
    lstMatchingNums = []
    lstLongerFile = longestFile(lstFirstFile,lstSecondFile)
    lstShortestFile = shortestFile(lstFirstFile,lstSecondFile)
    for eachLines in range(len(lstShortestFile)):
        lstLongerFile = longestfile(lstFirstFile,lstSecondFile)
        for eachLine in range(len(lstLongerFile)):
            if lstShortestFile[eachLines] == middleNumber(lstLongerFile):
               lstMatchingNums.append(lstShortestFile[eachLines])
               break
            elif lstShortestFile[eachLines] < middleNumber(lstLongerFile):
               lstLongerFile = lstLongerFile[0:len(lstLongerFile)//2+1]
               if len(lstLongerFile) <= 2 and lstLongerFile[0] == lstShortestFile[eachLines]:
                  lstMatchingNums.append(lstShortestFile[eachLines])
                  break
               elif middleNumber(lstLongerFile) != lstShortestFile[eachLines] and len(lstLongerFile) <=2:
                  break
            elif lstShortestFile[eachLines] > middleNumber(lstLongerFile):
                lstLongerFile = lstLongerFile[len(lstLongerFile)//2:]
                if len(lstLongerFile) <= 2 and lstLongerFile[0] == lstShortestFile[eachLines]:
                   lstMatchingNums.append(lstShortestFile[eachLines])
                   break
                elif middleNumber(lstLongerFile) != lstShortestFile[eachLines] and len(lstLongerFile) <= 2:
                   break
    return lstMatchingNums

lstHappyNums = open('happynumbs.txt','r')
lstReadingHappyLines = lstHappyNums.readlines()
lstHappyNums.close()
lstPrimeNumsFile = open('primenumbers.txt','r')
lstReadingPrimeLines = lstPrimeNumsFile.readlines()
lstPrimeNumsFile.close()
print(fileOverlap(lstReadingHappyLines,lstReadingPrimeLines))

如果我要运行该程序，它将给我一个空白列表，我不确定为什么。