Python学习_从文件读取数据和保存数据

2019-11-14 17:46:36

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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

>>> import os>>> 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 room for an 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>>> for each_line in data:    print(each_line,end='')    Man: Is this the right room for an 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 did not!Other Man: Oh I'm sorry, is this a five minute argument, or the full half hour?Man: Ah! (taking out his wallet and paying) Just the five minutes.Other Man: Just the five minutes. Thank you.Other Man: Anyway, I did.Man: You most certainly did not!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 it is!Man: No it isn't!(pause)Man: It's just contradiction!Other Man: No it isn't!Man: It IS!Other Man: It is NOT!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, this is futile!!(pause)Other Man: No it isn't!Man: Yes it is!>>> data.close()

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读取文件后，将不同role对应数据分别保存到列表man和other：

import osprint(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")    for each_line in data:        try:            (role, line_spoken)=each_line.split(':', 1)            line_spoken=line_spoken.strip()            if role=='Man':                man.append(line_spoken)            elif role=='Other Man':                other.append(line_spoken)        except ValueError:                pass    data.close()except IOError:    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：

 1 import os 2 print(os.getcwd()) 3 os.chdir('C:/Python33/HeadFirstPython/chapter3') 4 man=[] 5 other=[] 6  7 try: 8     data=open("sketch.txt") 9     for each_line in data:10         try:11             (role, line_spoken)=each_line.split(':', 1)12             line_spoken=line_spoken.strip()13             if role=='Man':14                 man.append(line_spoken)15             elif role=='Other Man':16                 other.append(line_spoken)17         except ValueError:18                 pass19     data.close()20 except IOError:21     print('The datafile is missing!')22 23 try:24     man_file=open('man.txt', 'w')      #以w模式访问文件man.txt25     other_file=open('other.txt','w')   #以w模式访问文件other.txt26     print (man, file=man_file)           #将列表man的内容写到文件中27     print (other, file=other_file)28 except IOError:29     print ('File error')30 finally:31     man_file.close()32     other_file.close()