python标准库介绍——24 traceback 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*
```