内容简介:01Python基础_09异常
1. try & except
原程序:
1 import math 2 3 while True: 4 text = raw_input('> ') 5 if text[0] == 'q': 6 break 7 x = float(text) 8 y = math.log10(x) 9 print "log10({0}) = {1}".format(x, y) View Code
这段代码接收命令行的输入,当输入为数字时,计算它的对数并输出,直到输入值为 q
为止。
但是当输入0或者负数时,会报错。
修改后的程序:
import math while True: try: text = raw_input('> ') if text[0] == 'q': break x = float(text) y = math.log10(x) print "log10({0}) = {1}".format(x, y) except ValueError: print "the value must be greater than 0" View Code
一旦 try
块中的内容出现了异常,那么 try
块后面的内容会被忽略, Python
会寻找 except
里面有没有对应的内容,如果找到,就执行对应的块,没有则抛出这个异常。
运行结果:
> -1 the value must be greater than 0 > 0 the value must be greater than 0 > 1 log10(1.0) = 0.0 > q View Code
捕捉所有类型错误:
将 except
的值改成 Exception
类,来捕获所有的异常。
import math while True: try: text = raw_input('> ') if text[0] == 'q': break x = float(text) y = 1 / math.log10(x) print "1 / log10({0}) = {1}".format(x, y) except Exception: print "invalid value" View Code
运行结果:
> 1 invalid value > 0 invalid value > -1 invalid value > 2 1 / log10(2.0) = 3.32192809489 > q View Code
进一步完善后的程序:
import math while True: try: text = raw_input('> ') if text[0] == 'q': break x = float(text) y = 1 / math.log10(x) print "1 / log10({0}) = {1}".format(x, y) except ValueError: print "the value must be greater than 0" except ZeroDivisionError: print "the value must not be 1" except Exception: print "unexpected error" View Code
运行结果:
> 1 the value must not be 1 > -1 the value must be greater than 0 > 0 the value must be greater than 0 > q View Code
2. finally
不管 try 块有没有异常, finally 块的内容总是会被执行,而且会在抛出异常前执行,因此可以用来作为安全保证,比如确保打开的文件被关闭。
try: print 1 / 0 finally: print 'finally was called.'
out: finally was called.
--------------------------------------------------------------------------- ZeroDivisionError Traceback (most recent call last) <ipython-input-13-87ecdf8b9265> in <module>() 1 try: ----> 2 print 1 / 0 3 finally: 4 print 'finally was called.' ZeroDivisionError: integer division or modulo by zero
如果异常被捕获了,在最后执行:
try: print 1 / 0 except ZeroDivisionError: print 'divide by 0.' finally: print 'finally was called.' out: divide by 0. finally was called. View Code
以上就是本文的全部内容,希望本文的内容对大家的学习或者工作能带来一定的帮助,也希望大家多多支持 码农网
猜你喜欢:本站部分资源来源于网络,本站转载出于传递更多信息之目的,版权归原作者或者来源机构所有,如转载稿涉及版权问题,请联系我们。