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HeadFirstPython学习_从文件读取数据和保存数据

2024-07-04 13:46:57   225人阅读

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=http://www.mamicode.com/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()
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：

import os
print(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=http://www.mamicode.com/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=http://www.mamicode.com/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                 pass
19     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.txt
25     other_file=open(‘other.txt‘,‘w‘)   #以w模式访问文件other.txt
26     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()

但是第26行print()为什么会报错？“syntax error while detecting tuple”


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