python下异常处理

  1 #encoding=utf-8
  2 
  3 """
  4 python遇到异常，程序直接运行
  5 try:
  6     "判断有可能抛出异常的代码"
  7     print "haha"
  8 except:
  9     "异常下运行的代码"
 10 else:
 11     "运行没有异常时候的逻辑"
 12 finally:
 13     "不管try判断如何，该代码总会执行"
 14 
 15 合理利用异常：
 16     1、不得不用的地方采用异常;
 17     2、正确使用异常：需要对异常进行捕获
 18      比如：except IOError:   
 19 
 20 """
 21 
 22 a = [1, 2, 3, 4, 5, 6]
 23 
 24 print a[4]
 25 
 26 try:
 27     print a[6]
 28 except:
 29     print u‘哈哈‘
 30 
 31 print "继续可以到这里"
 32 
 33 
 34 try:
 35     print a[6]
 36 except:
 37     print "huhu"
 38 else:
 39     print "hoho"
 40 finally:
 41     print "hehe"
 42     
 43     
 44 import urllib
 45 sth_url = "http://wsdfsdf"
 46 
 47 try:
 48     d = urllib.urlopen(sth_url)
 49 except:
 50     print "出错了"
 51 else:
 52     content = d.read()
 53 finally:
 54     pass
 55     #d.close()
 56     
 57 """
 58 异常的note：
 59     1、一个try对应一个except
 60     2、使用python内置异常，来对应自身情况；
 61     IOErro, IndexError
 62     3、捕获异常的办法：
 63         import logging
 64         logger = logging.getLogger()
 65         #logfile = ‘excetion_demo.log‘    #log文件名
 66         hdlr = logging.FileHandler(‘/tmp/sendlog.txt‘)
 67         formatter = logging.Formatter(‘%(asctime)s %(levelname)s %(message)s‘)
 68         hdlr.setFormatter(formatter)
 69         logger.addHandler(hdlr)  #logging绑定
 70         logger.setLevel(logging.NOTSET)
 71         
 72                
 73         import sys, logging
 74         try:
 75             d = urllib.urlopen("www.kdkdk.com")
 76         except:
 77             exc = sys.exc_info()
 78             loggin.debug(exc[1]
 79             print exc[1]
 80             print exc
 81     4、断言，assert
 82         assert 表达式，"出错后抛出message"
 83         assert 1>4,  "expression Error"
 84     先断言绝对不能发生的错误，然后在处理异常；
 85 """
 86 
 87 """
 88 with用法：自动回收垃圾
 89 #进入时，调用对象的__enter__
 90 #退出时，调用对象的__exit__函数
 91 
 92 d = open(‘a‘, ‘r‘)
 93 d.read()
 94 d.close()
 95 
 96 with open(‘a‘, ‘r‘)  as d:
 97     content = a.read()
 98 """
 99 
100 #with示例：
101 class sth(object):
102     def __init__(self, xixi):
103         self.a  = xixi
104         
105     def __enter__(self):
106         print u‘哈哈， 进来了‘
107         return self.a
108     
109     def __exit__(self, type, value, traceback):
110         print u‘哈哈，出去了‘
111 
112 with sth("gg") as s:
113     print s         #s为__enter__返回值
114 
115 """
116 定义自己的异常类
117 """
118 
119 class myException(Exception):
120     def __init__(self, error, msg):
121         self.args = (error, msg)
122         self.error = error
123         self.msg  = msg
124 
125 try:
126     raise myException(1, "my exception")
127 except Exception as e:
128     print str(e)