从零学python系列之从文件读取和保存数据

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
>>> 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()

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=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：

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模式访问文件man.txt
    other_file=open('other.txt','w')   #以w模式访问文件other.txt
    print (man, file=man_file)           #将列表man的内容写到文件中
    print (other, file=other_file)
except ioerror:
    print ('file error')
finally:
    man_file.close()
    other_file.close()

但是第26行print()为什么会报错？“syntax error while detecting tuple”，有大神能给解惑一下不