拓展：文件及错误处理1
拓展：文件及错误处理1
该部分为Head first python 第二部分内容。视频教程并未讲到，故作为拓展。
依样画葫芦来几段加深印象。
python从文件读取数据 open()方法
python中标准‘打开-处理-关闭’代码：
the_file = open('sketch.txt')
# do something with the data
#in 'the_file'
the_file.close()
需要导入os模块查看python目录位置
根据需要抽取数据行中的各个部分，比如，人物：对话内容。其中明显的分割符号是冒号‘：’，那么可以用split()方法实现。
如： each_line.split(':') 调用split()并关联each_line字符串，将字符串用‘：’分开。
split()方法返回一个字串符列表，这会赋至一个目标标识符列表，称之为 多重赋值（multiple assignment）如：
(role,line_spoken) = each_line.split(':')
照着书本这样写：
这下跟教材里的范例一模一样了。。它的print有三行。。。我在想能不能格式化字符串用%s代替输出？！
依样画葫芦来几段加深印象。
python从文件读取数据 open()方法
python中标准‘打开-处理-关闭’代码：
the_file = open('sketch.txt')
# do something with the data
#in 'the_file'
the_file.close()
需要导入os模块查看python目录位置
>>> import os #从标准库导入os
>>> os.getcwd()
'D:\\Python33' #当前的工作目录
>>> os.chdir ('f:\\python') #修改为包含数据文件的文件夹
>>> os.getcwd() #确认现在在正确的目录下
'f:\\python'
>>> data = open('sketch.txt') #把打开的文件内容赋值给data
>>> print (date.readline(), end = '') #使用readline()方法从文件中获取一个数据行，然后打印出来看看。
Man: Is this the right room for an argument?
>>> print (date.readline(), end = '')
Other Man: I've told you once.
>>> print (date.readline(), end = '')
Man: No you haven't!
>>> print (date.readline(), end = '')
Other Man: Yes I have.
>>>
读取成功
返回到文件起始位置，使用for循环处理文件中的每一行：
>>> data.seek(0) #用seek()方法返回到文件的起始位置
0
>>> for each_line in data: #标准的for循环迭代
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!
...
Other Man: Nonsense!
Man: (exasperated) Oh, this is futile!!
(pause)
Other Man: No it isn't!
Man: Yes it is!
>>> data.close() #养成良好的习惯，处理完文件就要将它关闭。
如： each_line.split(':') 调用split()并关联each_line字符串，将字符串用‘：’分开。
>>> each_line.split (':')
['Man', ' Yes it is!\n']
(role,line_spoken) = each_line.split(':')
照着书本这样写：
>>> for each_line in data:
(role, line_spoken) = each_line.split(':')
print(role, end = '')
print(' said: ', end = '')
print(line_spoken , end = '')
>>>
怎么回事？跟结果不一样啊。。。输入之后没反应，直接返回shell命令行。。。
摸了很久才知道，原来文件刚才被读取过关闭了，要重新打开
摸了很久才知道，原来文件刚才被读取过关闭了，要重新打开
>>> data = open('sketch.txt')
>>> for each_line in data:
(role, line_spoken) = each_line.split(':')
print(role , end = '')
print (' said: ', end = '')
print (line_spoken, end = '')
Man said: Is this the right room for an argument?
Other Man said: I've told you once.
Man said: No you haven't!
Other Man said: Yes I have.
Man said: When?
Other Man said: Just now.
Man said: No you didn't!
Other Man said: Yes I did!
Man said: You didn't!
Other Man said: I'm telling you, I did!
Man said: You did not!
Other Man said: Oh I'm sorry, is this a five minute argument, or the full half hour?
Man said: Ah! (taking out his wallet and paying) Just the five minutes.
Other Man said: Just the five minutes. Thank you.
Other Man said: Anyway, I did.
Man said: You most certainly did not!
Traceback (most recent call last):
File "<pyshell#64>", line 2, in <module>
(role, line_spoken) = each_line.split(':')
ValueError: too many values to unpack (expected 2)
>>> data = open('sketch.txt')
>>> for each_line in data:
(role, line_spoken) = each_line.split(':')
print('%s said: %s' % (role, line_spoken) , end = '' )
Man said: Is this the right room for an argument?
Other Man said: I've told you once.
Man said: No you haven't!
Other Man said: Yes I have.
Man said: When?
Other Man said: Just now.
Man said: No you didn't!
Other Man said: Yes I did!
Man said: You didn't!
Other Man said: I'm telling you, I did!
Man said: You did not!
Other Man said: Oh I'm sorry, is this a five minute argument, or the full half hour?
Man said: Ah! (taking out his wallet and paying) Just the five minutes.
Other Man said: Just the five minutes. Thank you.
Other Man said: Anyway, I did.
Man said: You most certainly did not!
Traceback (most recent call last):
File "<pyshell#76>", line 2, in <module>
(role, line_spoken) = each_line.split(':')
ValueError: too many values to unpack (expected 2)
>>>
这叫学以致用。
看到这代码中返回一个Traceback的错误，类型是ValueError：大概是说给的值多了，前面spilt()的方法只能用冒号分解成两部分。
这是教材里的范例。下节课将分析这些错误。
看到这代码中返回一个Traceback的错误，类型是ValueError：大概是说给的值多了，前面spilt()的方法只能用冒号分解成两部分。
这是教材里的范例。下节课将分析这些错误。
