python标准库介绍——24回溯模块详解

==traceback 模块== [Example 2-18 #eg-2-18] 展示了 ``traceback`` 模块允许你在程序里打印异常的跟踪返回 (Traceback)信息, 类似未捕获异常时解释器所做的. 如 [Example 2-18 #eg-2-18] 所示. ====Example 2-18. 使用 traceback 模块打印跟踪返回信息====[eg-2-18] ``` File: traceback-example-1.py # note! importing the traceback module messes up the # exception state, so you better do that here and not # in the exception handler # 注意! 导入 traceback 会清理掉异常状态, 所以 # 最好别在异常处理代码中导入该模块 import traceback try: raise SyntaxError, 'example' except: traceback.print_exc() *B*Traceback (innermost last): File 'traceback-example-1.py', line 7, in ? SyntaxError: example*b* ``` [Example 2-19 #eg-2-19] 使用 ``StringIO`` 模块将跟踪返回信息放在字符串中. ====Example 2-19. 使用 traceback 模块将跟踪返回信息复制到字符串====[eg-2-19] ``` File: traceback-example-2.py import traceback import StringIO try: raise IOError, 'an i/o error occurred' except: fp = StringIO.StringIO() traceback.print_exc(file=fp) message = fp.getvalue() print 'failure! the error was:', repr(message) *B*failure! the error was: 'Traceback (innermost last):12 File 'traceback-example-2.py', line 5, in ?12IOError: an i/o error occurred012'*b* ``` 你可以使用 ``extract_tb`` 函数格式化跟踪返回信息, 得到包含错误信息的列表, 如 [Example 2-20 #eg-2-20] 所示. ====Example 2-20. 使用 traceback Module 模块编码 Traceback 对象====[eg-2-20] ``` File: traceback-example-3.py import traceback import sys def function(): raise IOError, 'an i/o error occurred' try: function() except: info = sys.exc_info() for file, lineno, function, text in traceback.extract_tb(info[2]): print file, 'line', lineno, 'in', function print '=>', repr(text) print '** %s: %s' % info[:2] *B*traceback-example-3.py line 8 in ? => 'function()' traceback-example-3.py line 5 in function => 'raise IOError, 'an i/o error occurred'' ** exceptions.IOError: an i/o error occurred*b* ```