python核心编程第二版第三章习题

3–11.
字符串格式化 不再抑制 readTextFile.py 中 print 语句生成的 NEWLINE 字符，修改你的
代码， 在显示一行之前删除每行末尾的空白。这样， 你就可以移除 print 语句末尾的逗号了。
提示： 使用字符串对象的 strip()方法
                       
3–12. 合并源文件。将两段程序合并成一个，给它起一个你喜欢的名字，比方
readNwriteTextFiles.py。让用户自己选择是创建还是显示一个文本文件。
3–13. 添加新功能。将你上一个问题改造好的 readNwriteTextFiles.py 增加一个新功
能：允许用户编辑一个已经存在的文本文件。 你可以使用任何方式，无论是一次编辑一行，还
是一次编辑所有文本。需要提醒一下的是， 一次编辑全部文本有一定难度，你可能需要借助 GUI
工具包或一个基于屏幕文本编辑的模块比如 curses 模块。要允许用户保存他的修改（保存到
文件）或取消他的修改（不改变原始文件），并且要确保原始文件的安全性（不论程序是否正
常关闭）。

import os
ls=os.linesep
#get filename

def write_Text():
    
    fname=raw_input(">>")
    while True:
        if os.path.exists(fname):
            print "ERROR:'%S' already exists" % fname
        else:
            break
    all=[]
    print "/nEnter lines('.' by itself to quit).\n"
    while True:
        entry=raw_input('>')
        if entry=='.':
            break
        else:
            all.append(entry)
    #write lines to file with proper line-ending
    fobj=open(fname,'w')
    #fobj.writelines(['%s%s' % (x,ls) for x in all])
    fobj.writelines([x+ls for x in all])
    fobj.close()
    print'DONE!'
    
def read_Text():
    fname=raw_input("Enter filename:")
    print
    
    try:
        fobj=open(fname,'r')
    except IOError,e:
        print "*** file open error:",e
    else:
        #display contents to the screen
        
        for eachLine in fobj:
            eachLine=eachLine.strip().strip(',')
            print eachLine
            
        fobj.close()    

def modify_text():
    fname=raw_input("Enter filename:")
    fobj=open(fname,'r+')
    lis=fobj.readlines()
    i=0
    for eachline in lis:
        eachline=eachline.strip()
        print str(i)+" "+eachline
        i+=1
    while True:
        
        print "which line you want to modify:"
        num=raw_input(">>")
        num=int(num)    
        lis[num]=raw_input("write new content:")+'\n'
        fobj=open(fname,'w+')
        fobj.writelines(lis)
        fobj.close()
        print "modifiy sucess"
        choice=raw_input("exit? y/n:")
        if choice=="n":
            break
        else:
            continue
    

while True:
    print
    
    print "choice 1,write file"
    print "choice 2,read file"  
    print "choice 3,modify file"
    print
    
    choice=raw_input("please make a choice:")
    if choice=="1":
        write_Text()
    elif choice=="2":
        read_Text()
    elif choice=="3":
        modify_text()
    else:
        print "please enter 1 or 2"

　　

 修改后：

import os
ls=os.linesep
#get filename

def write_Text():
    
    fname=raw_input("filename:")
    
    while os.path.exists(fname):
        print "ERROR:'%S' already exists" % fname
    all=[]
    print "/nEnter lines('.' by itself to quit).\n"
    entry=raw_input(">>")
    while entry!=".":
        all.append(entry)
        entry=raw_input('>')
    #write lines to file with proper line-ending
    fobj=open(fname,'w')
    #fobj.writelines(['%s%s' % (x,ls) for x in all])
    fobj.writelines([x+ls for x in all])
    fobj.close()
    print'DONE!'
    make_choice()
    
def read_Text():
    fname=raw_input("Enter filename:")
    print "\n"
    
    try:
        fobj=open(fname,'r')
    except IOError,e:
        print "*** file open error:",e
    else:
        #display contents to the screen
        
        for eachLine in fobj:
            eachLine=eachLine.strip().strip(',')
            print eachLine
            
        fobj.close() 
    make_choice()

def modify_text():
    fname=raw_input("Enter filename:")
    fobj=open(fname,'r+')
    lis=fobj.readlines()
    i=0
    for eachline in lis:
        eachline=eachline.strip()
        print str(i)+" "+eachline
        i+=1
    
    choice="n"
    while choice=="n":
        print "which line you want to modify:"
        num=raw_input(">>")
        num=int(num)    
        lis[num]=raw_input("write new content:")+'\n'
        choice=raw_input("exit? y/n:")
    fobj=open(fname,'w+')
    fobj.writelines(lis)
    fobj.close()
    print "modifiy sucess"   
    make_choice
       
def make_choice():
    print "\n"
    print "choice 1,write file"
    print "choice 2,read file"  
    print "choice 3,modify file"
    print "\n"
    choice=raw_input("please make a choice:")
    if choice=="1":
        write_Text()
    elif choice=="2":
        read_Text()
    elif choice=="3":
        modify_text()
    else:
        print "please enter 1 or 2 or 3"    
       
       
make_choice()