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從零學(xué)python系列之從文件讀取和保存數(shù)據(jù)

更新時(shí)間：2014年05月23日 10:23:38 作者：

在Python一般都是運(yùn)用內(nèi)置函數(shù)open()與文件進(jìn)行交互，下面說說具體用法

在HeadFirstPython網(wǎng)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(dǎo)入os模塊，并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(dāng)前工作目錄
'C:\\Python33'
>>> os.chdir('C:/Python33/HeadFirstPython/chapter3')   #切換包含數(shù)據(jù)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”，讀取并顯示前兩行：

復(fù)制代碼代碼如下:

>>> 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(guān)閉文件：

復(fù)制代碼代碼如下:

>>> data.seek(0) #使用seek()方法回到文件起始位置
>>> 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(yīng)數(shù)據(jù)分別保存到列表man和other：

復(fù)制代碼代碼如下:

import os
print(os.getcwd())
os.chdir('C:\Python33\HeadFirstPython\chapter3')
man=[] #定義列表man接收Man的內(nèi)容
other=[] #定義列表other接收Other Man的內(nèi)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(shí)，默認(rèn)的訪問模式為r，表示讀，不需要特意指定；

要打開一個(gè)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(jīng)存在則會清空現(xiàn)有內(nèi)容；

要追加到一個(gè)文件，需要指定模式a，不會清空現(xiàn)有內(nèi)容；

要打開一個(gè)文件完成寫和讀，且不清空現(xiàn)有內(nèi)容，需要指定模式w+；

例如，將上例中保存的man和other內(nèi)容以文件方式保存時(shí)，可修改如下：

復(fù)制代碼代碼如下:

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(nèi)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(bào)錯(cuò)？“syntax error while detecting tuple”，有大神能給解惑一下不

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