python读写文件的脚本

一个python读写文件脚本，代码如下：

   import os
    ls=os.linesep

    numlist=['1','2','3']
    def getnum():
        input=raw_input('''
    ---------------------
            1.read
            2.write
            3.quit
    ---------------------
    enter your select num:n''')
        if input in numlist:
            return input
        else:
            print 'enter error,input again'
            return getnum()

    def getfile():
        file=raw_input('enter filename:n')
        return file

    def comment():
        print 'enter "quit" to exit'
        lines=[]
        line=raw_input('>')
        while True:
            if line=='quit':
                return lines
            else:
                lines.append(line)
                line=raw_input('>')

    def write():
        if os.path.exists(file):
            f=open(file,'a')
            f.writelines(['%s%s'%(x,ls) for x in com])
            f.close()
            print 'append done'
        else:
            f=open(file,'w')
            f.writelines(['%s%s'%(x,ls) for x in com])
            f.close()
            print 'write done'

    def read():
        if os.path.exists(file):
            f=open(file,'r')
            for line in f:
                print line,
        else:
            print 'file is not exists'
    while True:
        num=getnum()
        if num=='1':
            file=getfile()
            read()
        elif num=='2':
            file=getfile()
            com=comment()
            write()
        else:
            print 'exit'
            break