python写文件、读取文件、按行修改文件

#!/usr/bin/env python # -*- coding: utf-8 -*-'''Created on 2012-11-29@author: Eliotmake and read a file'''import osls = os.linesep;def makefile():    #input the file name    while True:        aFileName = raw_input('Enter a file Name:')        if os.path.exists(aFileName):            print '%s already exists!' % (aFileName)        else:            break    #input the file text    text = []    print "\nEnter lines ('.' by itself to quit).\n"    while True:        entry = raw_input('>')        if entry == '.':            break        else:            text.append(entry)    #input the file    file = open(aFileName, 'w')    file.writelines(['%s%s' % (x, ls) for x in text])    file.close()    print 'Make file over!'def readfile():    #input the file name    while True:        fileName = raw_input('Enter a file Name to read:')        if os.path.exists(fileName):            break        else:            print 'The file is not exists!'    #read the file    file = open(fileName, 'r')    for x in file:        print x,    file.close()    print 'Read file over!'def Modify():    #input the file name    while True:        mFileName = raw_input('Enter a file name:')        if os.path.exists(mFileName):            break        else:            print 'The file is not exists!'    #modify the file    fileRead = open(mFileName, 'r')    lines = fileRead.readlines()    fileRead.close()        fileWrite = open(mFileName, 'w')    for line in lines:        '''        if line.strip().startswith('XYW'):            insert = raw_input('Enter text:') + ls            fileWrite.write(insert)        else:            fileWrite.write(line)        '''        print '%s' % line                insert = raw_input('>:') + ls        fileWrite.write(insert)    fileWrite.close()def main():    while True:        print '1.make file 2.read file 3.modify file 4.exit'        ch = int(raw_input(':'))        if ch == 1:            makefile()        elif ch == 2:            readfile()        elif ch == 3:            Modify()        else:            break    print 'The game is over!'if __name__ == '__main__':    main()