python学习笔记四（数据持久储存）

第四章刚开始，提出要把sktch.txt 中Man和Othe Man的台词分别储存在两个不同的list里。

刚开始的代码为：

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
except IOError:
    print 'the txt is missing'
print man
print other

其中值得一提的是两个异常的处理。外层的异常是指如果sketch文件不存在时，抛出来的异常为‘the txt is missing’.内层的异常是针对split方法调用时如果没有value值，时执行pass,即忽略不计。

而后，需要把man 和other的分别存储在不同的txt里。这里的代码如下：

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
except IOError:
    print('the txt is missing')
                                                                                                                                                                                                                                                                                                                                        
try:
        man_part = open('man_part.txt','w')
        other_part =open('other_part.txt','w')
        print(man,file = man_part)
        print(other,file = other_part)
        man_part.close()
        other_part.close()
except IOError:
        print('file error')

说明：

        自此由于书上是按照 Python3 介绍的，写入文件的方法和Python2不兼容,所以为了方便，我Python的版本也自动改为了3.3.

书上紧接着介绍了finally 格式。

finally是配合try/except使用的，即是无论执行其中哪一种代码，则finally都会执行。

 结合此例，则是关闭文件适合执行finally.如下：

finally:
        man_part.close()
        other.part.close()

之后又提到了如何显示错误信息。用的标识符是err.

试验一下：

我写了一个Missingtxt.py

try:
        man_part = open('man_part.txt')
                                                                                                                                                                                 
        man_part.close()
except IOError as err:
        print('file error:' +str(err))

with的使用

with的使用可以取代finally。

例如上述的例子可以改写为：

try:
       with open('man_part.txt','w') as man_part:
            print(man,file = man_part)
       with open('other_part.txt','w') as other_part:     
            print(other,file = other_part)
except IOError:
        print('file error')

Pickle:

   pickle是持久储存的作用，是python专有的格式。断电后仍不消失。

import pickle
with open('mydata.pickle','wb') as mysavedata:
    pickle.dump([1,2,'data'], mysavedata)
with open('mydata.pickle','rb') as mystoredata:
    alist = pickle.load(mystoredata)
    print(alist)

由此改写上述的程序：

import pickle
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
except IOError:
    print('the txt is missing')
        
try:
    try:
        with open('man_part.txt','wb') as man_part:
            pickle.dump(man,man_part)
        with open('other_part.txt','wb') as other_part:     
            pickle.dump(other,other_part)
    except PickleError as perr:
        print('pickling error'+ str(perr))
except IOError as err:
    print('file error'+ str(err))