运用Python中的内置函数open()与文件进行交互
在HeadFirstPython网站中下载所有文件，解压后以chapter 3中的“sketch.txt”为例：
新建IDLE会话，首先导入os模块，并将工作目录却换到包含文件“sketch.txt”的文件夹，如C:\\Python33\\HeadFirstPython\\chapter3
>>>importos>>> os.getcwd()#查看当前工作目录'C:\\Python33'>>> os.chdir('C:/Python33/HeadFirstPython/chapter3')#切换包含数据文件的文件夹>>> os.getcwd()#查看切换后的工作目录'C:\\Python33\\HeadFirstPython\\chapter3'
打开文件“sketch.txt”，读取并显示前两行：
>>> data=open('sketch.txt')>>>PRint(data.readline(),end='')
Man: Is this the right roomforan argument?>>>print(data.readline(),end='')
Other Man: I've told you once.
回到文件起始位置，使用for语句处理文件中的每行，最后关闭文件：
>>> data.seek(0)#使用seek()方法回到文件起始位置0>>>foreach_lineindata:print(each_line,end='')
Man: Is this the right roomforan argument?
Other Man: I've told you once.Man: No you haven't!Other Man: Yes I have.
Man: When?
Other Man: Just now.
Man: No you didn't!Other Man: Yes I did!
Man: You didn't!Other Man: I'm telling you, I did!Man: You didnot!
Other Man: Oh I'm sorry, is this a five minute argument, or the full half hour?Man: Ah! (taking out his walletandpaying) Just the five minutes.
Other Man: Just the five minutes. Thank you.
Other Man: Anyway, I did.
Man: You most certainly didnot!
Other Man: Now let's get one thing quite clear: I most definitely told you!Man: Oh no you didn't!Other Man: Oh yes I did!
Man: Oh no you didn't!Other Man: Oh yes I did!
Man: Oh look, this isn't an argument!(pause)
Other Man: Yes itis!
Man: No it isn't!(pause)
Man: It's just contradiction!Other Man: No it isn't!Man: It IS!
Other Man: ItisNOT!
Man: You just contradicted me!
Other Man: No I didn't!Man: You DID!
Other Man: No no no!
Man: You did just then!
Other Man: Nonsense!
Man: (exasperated) Oh, thisisfutile!!
(pause)
Other Man: No it isn't!Man: Yes itis!>>> data.close()
View Code
读取文件后，将不同role对应数据分别保存到列表man和other：
importosprint(os.getcwd())
os.chdir('C:\Python33\HeadFirstPython\chapter3')
man=[]#定义列表man接收Man的内容other=[]#定义列表other接收Other Man的内容try:
data=open("sketch.txt")foreach_lineindata:try:
(role, line_spoken)=each_line.split(':', 1)
line_spoken=line_spoken.strip()ifrole=='Man':
man.append(line_spoken)elifrole=='Other Man':
other.append(line_spoken)exceptValueError:passdata.close()exceptIOError:print('The datafile is missing!')print(man)print(other)
Tips:
使用open()方法打开磁盘文件时，默认的访问模式为r，表示读，不需要特意指定；
要打开一个文件完成写，需要指定模式w，如data=open("sketch.txt","w")，如果该文件已经存在则会清空现有内容；
要追加到一个文件，需要指定模式a，不会清空现有内容；
要打开一个文件完成写和读，且不清空现有内容，需要指定模式w+；
例如，将上例中保存的man和other内容以文件方式保存时，可修改如下：
1importos2print(os.getcwd())3os.chdir('C:\Python33\HeadFirstPython\chapter3')4man=[]5other=[]67try:8data=open("sketch.txt")9foreach_lineindata:10try:11(role, line_spoken)=each_line.split(':', 1)12line_spoken=line_spoken.strip()13ifrole=='Man':14man.append(line_spoken)15elifrole=='Other Man':16other.append(line_spoken)17exceptValueError:18pass19data.close()20exceptIOError:21print('The datafile is missing!')2223try:24man_file=open('man.txt','w')#以w模式访问文件man.txt25other_file=open('other.txt','w')#以w模式访问文件other.txt26print(man, file=man_file)#将列表man的内容写到文件中27print(other, file=other_file)28exceptIOError:29print('File error')30finally:31man_file.close()32other_file.close()
但是第26行print()为什么会报错？“syntax error while detecting tuple”