【Python基础教程】第8章 异常

1.自定义异常：继承Exception

#1.自定义异常类#方法：从Exception类继承class SomeCustomException(Exception):pass

2.处理异常

#(1)捕捉异常:try/excepttry:    x = input('Enter the first number:')    y = input('Enter the second number:')    print x/yexcept ZeroDivisionError:    print "The second number couldm't be zero"#注：如果异常没有被捕捉，就会传递到函数调用的地方。#    如果一直没有被捕捉，会一直传到程序的最顶层。#    最终，在Trackback中打印输出。#(2)传递异常:raiseclass MuffledCalculator:    muffled = False    def calc(self, expr):        try:            return eval(expr)        except ZeroDivisionError:            if self.muffled:                print 'Division by zero is illegal'            else:                raise#将异常传递#(3)多个异常#(3.1)except ZeroDivisionError:print "......"except TypeError:print "......"#(3.2)except (ZeroDivisionError, TypeError), e:print e#(4):捕捉全部异常:仅仅使用except(很危险，不提倡使用)try:    x = input('Enter the first number:')    y = input('Enter the second number:')    print x/yexcept:    print "Something wrong happened.."#(5)try/except 和 elsewhile True:    try:        x = input('Enter the first number:')        y = input('Enter the second number:')        value = x/y        print 'x/y is', value    except Exception, e:        print "The input is invalid"        print "Please try again"    else:        break#注：except语句和else语句仅仅会执行一个。#    当发生异常，不执行else；当没有反生异常，执行else#(5)finallytry:    1/0except NameError:    print 'Unknown variable'else:    print 'That went well'finally:    print 'other things'