异常处理

检测文件名是否正确，然后按行读取文件，否则循环输入文件名直至正确。

def processFile(dataFile):
    count = 1
    for item in dataFile:
        print('Line '+ str(count) + ':' + item.strip())
        count = count + 1

while True:
    try:
        fileName = input('Input a file name to open: ')
        dataFile = open(fileName,'r')
    except IOError:
        print('Bad file name; try again')
    else:
        processFile(dataFile)
        break
    finally:
        try:
            dataFile.close()
        except NameError:
            print('Going around again')