六、Python：异常

该章来通过例子了解一下Python中的异常

#1、当未捕获到异常时，执行else语句
try: 
    f=file("a.txt","r")
    while True:
        line = f.readline()
        if len(line) == 0:
            break
        print line
    else: 
        print "read end!",
    f.close()
except IOError:
    print "file is't exist!"
except Exception:
    print "have error!"
else:
    print "all is ok"
    
#例子1：捕捉所有异常  
a = 3
b = 4
c = 5

try:
    a=b
    b=c
except Exception ,data :
    print Exception ,":",data 
    
    
#例子2：采用traceback模块查看异常，需要导入traceback模块
import sys
try:
    a = b
    b = c
except:
    import traceback
    print traceback.print_exc()
    
#例子3：采用sys模块回溯最后的异常
try:
    a = b
    b = c
except:
    info = sys.exc_info()
    print len(info)
    print info
    print info[0]
    print info[1]

#例子4：finally 语句,不管有没有发生异常都将执行finally语句块。
try:
    a= 3/1
finally:
    print "exec finally"
    
#例子5：try-except-finally
import sys
try:
    a=3/0
except ZeroDivisionError:
    print 'error'
finally:
    print "stop exec"

try:
    a=5/0 
except:
    print sys.exc_info()[1]
finally:
    print "stop exec"

#例6：引发异常
class MyError( Exception ):
    pass

try:
    raise MyError     #自己抛出一个异常
except MyError:
    print 'a error'