python笔记 2008-08-21 exception pep

exception 语法

书上的exception语法在python3.6 不通过。测试实际如下:

    try:
        filename = input('enter file name:') 
        fobj = open(filename,'a')
        i = 1;
        for eachLine in fobj:
            print('Line%i:' % i,eachLine,end='')
            i += 1
        fobj.close()
    except IOError as e:
        print ('Sorry, file open error', e)

PEP

https://www.python.org/dev/peps/

Python 增强提案(Python Enhancement Proposal)

一串字符串转化为数字列表

>>> x=input()
1 2 3 4
>>> xlist=x.split(" ")
>>> print(xlist)
['1', '2', '3', '4']
>>> xlist = [int(xlist[i]) for i in range(len(xlist))]
>>> print(xlist)
[1, 2, 3, 4]

赋值

在赋值时，不管这个对象是新创建的，还
是一个已经存在的，都是将该对象的引用（并不是值）赋值给变量

增量赋值，如果对象是可变的则对象还是原来的引用

>>> aList=[2,'b']
>>> id(aList)
46249024
>>> aList += [5]
>>> aList
[2, 'b', 5]
>>> id(aList)
46249024  #增量赋值，引用还是同一个
>>> aList = aList +[99]
>>> aList
[2, 'b', 5, 99]
>>> id(aList)
46399736  #非增量赋值，aList的引用变成了另一个