Python學習_從文件讀取數據和保存數據

運用Python中的內置函數open()與文件進行交互

在HeadFirstPython網站中下載所有文件，解壓后以chapter 3中的“sketch.txt”為例：

新建IDLE會話，首先導入os模塊，並將工作目錄卻換到包含文件“sketch.txt”的文件夾，如C:\\Python33\\HeadFirstPython\\chapter3

>>> import os
>>> os.getcwd()    #查看當前工作目錄
'C:\\Python33'
>>> os.chdir('C:/Python33/HeadFirstPython/chapter3')   #切換包含數據文件的文件夾
>>> os.getcwd()     #查看切換后的工作目錄
'C:\\Python33\\HeadFirstPython\\chapter3'

 打開文件“sketch.txt”，讀取並顯示前兩行：

>>> 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語句處理文件中的每行，最后關閉文件：

>>> 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()

 

 讀取文件后，將不同role對應數據分別保存到列表man和other：

import os
print(os.getcwd())
os.chdir('C:\Python33\HeadFirstPython\chapter3')
man=[]    #定義列表man接收Man的內容
other=[]  #定義列表other接收Other Man的內容

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()方法打開磁盤文件時，默認的訪問模式為r，表示讀，不需要特意指定；

要打開一個文件完成寫，需要指定模式w，如data=open("sketch.txt","w")，如果該文件已經存在則會清空現有內容；

要追加到一個文件，需要指定模式a，不會清空現有內容；

要打開一個文件完成寫和讀，且不清空現有內容，需要指定模式w+；

 

 例如，將上例中保存的man和other內容以文件方式保存時，可修改如下：

import os
print(os.getcwd())
os.chdir('C:\Python33\HeadFirstPython\chapter3')
man=[]
other=[]

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!')

try:
    man_file=open('man.txt', 'w')      #以w模式訪問文件man.txt
    other_file=open('other.txt','w')   #以w模式訪問文件other.txt
    print (man, file=man_file)           #將列表man的內容寫到文件中
    print (other, file=other_file)
except IOError:
    print ('File error')
finally:
    man_file.close()
    other_file.close()

但是第26行print()為什么會報錯？“syntax error while detecting tuple”