traceback异常打印

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traceback模块

traceback模块被用来跟踪异常返回信息. 如下例所示:

import traceback
try:
raise SyntaxError, "traceback test"
except:
traceback.print_exc()

将会在控制台输出类似结果:

Traceback (most recent call last):
File "H:PythonWorkSpaceTestsrcTracebackTest.py", line 3, in <module>
raise SyntaxError, "traceback test"
SyntaxError: traceback test

类似在你没有捕获异常时候, 解释器所返回的结果.

你也可以传入一个文件, 把返回信息写到文件中去, 如下:

import traceback
import StringIO
try:
raise SyntaxError, "traceback test"
except:
fp = StringIO.StringIO() #创建内存文件对象
traceback.print_exc(file=fp)
message = fp.getvalue()
print message

常用方法及其区别

问题：traceback.print_exc()和traceback.format_exc()有什么区别呢？

format_exc()返回字符串，print_exc()则直接给打印出来。

即traceback.print_exc()与print traceback.format_exc()效果是一样的。

print_exc()还可以接受file参数直接写入到一个文件。比如

traceback.print_exc(file=open('tb.txt','w+'))

写入到tb.txt文件去。

正文测试过程

#sys.exc_info()
返回 (type, value, traceback). type为异常类型, value为异常的参数(通常为异常错误的信息), traceback为跟踪回溯的对象.

exc_type, exc_value, exc_traceback = sys.exc_info() print "*** print sys.exc_info:" print 'exc_type is: %s, exc_value is: %s, exc_traceback is: %s' % (exc_type, exc_value, exc_traceback)

输出:

*** print sys.exc_info: exc_type is: <type 'exceptions.IndexError'>, exc_value is: tuple index out of range, exc_traceback is: <traceback object at 0x7fee3b00eb48>

traceback.print_tb(traceback[, limit[, file]])

打印栈的跟踪信息. 如果省略limit, 将打印所有跟踪入口信息. file默认为std.err.

import traceback
import sysdef traceback_test():
try:
raise SyntaxError, 'traceback_test'
except Exception as e:
traceback.print_tb(e, limit=1, file=sys.stdout)if __name__ == '__main__':
traceback_test()

错误信息

Traceback (most recent call last):
File "D:/MH_code/test_flask_project/app/traceback.py", line 14, in <module>
traceback_test()
File "D:/MH_code/test_flask_project/app/traceback.py", line 11, in traceback_test
traceback.print_tb(e, limit=1, file=sys.stdout)
File "C:\Python27\lib\traceback.py", line 61, in print_tb
f = tb.tb_frame
AttributeError: 'exceptions.SyntaxError' object has no attribute 'tb_frame'

traceback.print_exception(type, value, traceback[, limit[, file]])

打印异常信息. (type, value, traceback)为sys.exc_info()返回的元组.和print_tb不同的是:
- 如果traceback不为空, 打印栈头信息(即最近被调用的信息).
- 在栈的信息后打印异常类型和参数.
- 如果是语法错误, 会打印对应的代码行数, 用”^”指明语法错误的位置.

import traceback
import sysdef traceback_test():
try:
raise SyntaxError, 'traceback_test'
except Exception as e:
exc_type, exc_value, exc_traceback = sys.exc_info()
traceback.print_exception(exc_type, exc_value, exc_traceback, limit=2, file=sys.stdout)if __name__ == '__main__':
traceback_test()

错误信息

None（用的2.7，打印的什么玩意没细究）

traceback.print_exc([limit[, file]])

print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)的简写

import traceback
import sysdef traceback_test():
try:
raise SyntaxError, 'traceback_test'
except Exception as e:
traceback.print_exc()if __name__ == '__main__':
traceback_test()

错误信息

Traceback (most recent call last):
File "D:/MH_code/test_flask_project/app/traceback.py", line 11, in traceback_test
raise SyntaxError, 'traceback_test'
SyntaxError: traceback_test

traceback.format_exc([limit])

类似于print_exc(limit), 但是返回字符串而不是输出到file.

import traceback
import sysdef traceback_test():
try:
raise SyntaxError, 'traceback_test'
except Exception as e:
formatted_lines = traceback.format_exc().splitlines()
print formatted_lines[0]
print formatted_lines[-1]
if __name__ == '__main__':
traceback_test()

错误信息

Traceback (most recent call last):
SyntaxError: traceback_test

traceback.format_exception(type, value, tb[, limit])

格式化栈信息和异常信息. 返回一个列表, 包括代码文件和代码行, 以及异常信息.

import traceback
import sysdef traceback_test():
try:
raise SyntaxError, 'traceback_test'
except Exception as e:
exc_type, exc_value, exc_traceback = sys.exc_info()
print repr(traceback.format_exception(exc_type, exc_value, exc_traceback))
if __name__ == '__main__':
traceback_test()

错误信息

['None\n']

traceback.extract_tb(traceback[, limit])

返回一个跟踪对象(traceback)的元组列表. 元组内容为(filename, line number, function name, text).

import traceback
import sysdef traceback_test():
try:
raise SyntaxError, 'traceback_test'
except Exception as e:
exc_type, exc_value, exc_traceback = sys.exc_info()
print repr(traceback.extract_tb(exc_traceback))
if __name__ == '__main__':
traceback_test()

错误信息

[('D:/MH_code/test_flask_project/app/traceback.py', 11, 'traceback_test', "raise SyntaxError, 'traceback_test'")]

traceback.extract_stack([f[, limit]])

返回当前栈帧的原始跟踪(traceback)对象的信息, 格式和extract_tb一样, 元组内容为(filename, line number, function name, text).

import traceback
import sysdef traceback_test():
try:
raise SyntaxError, 'traceback_test'
except Exception as e:
print traceback.extract_stack()
if __name__ == '__main__':
traceback_test()

输出

[('D:/MH_code/test_flask_project/app/traceback.py', 22, '<module>', 'traceback_test()'),
('D:/MH_code/test_flask_project/app/traceback.py', 20, 'traceback_test', 'print
traceback.extract_stack()')]

traceback.format_list(list)

按照list对应的项, 返回一个元组列表, 形式为同extract_tb()或者extract_stack()返回的一样. 元组内容为(filename, line number, function name, text)
将extract_tb()或者extract_stack()返回的list进行格式化.