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: Eliot
make and read a file
'''
import os
ls = 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()