使用模块traceback捕捉exception

使用模块 traceback
结合sys.exc_info()的输出（type, value, traceback）:
    type为出错的exception类型;
    value 为具体为对应exception的错误描述信息;
    traceback 为返回的该处exception的1个traceback类型；

try:
    a = b+ c
except:
    t, v, tb = sys.exc_info()
    errstr = StringIO.StringIO()  
   
    test_tb = traceback.print_exception(t,v,tb,file=errstr)  
    print errstr.getvalue()
    errstr.close()
    #输出到file handle,结果为
Traceback (most recent call last):
  File "1.py", line 4, in
    a = b+ c
NameError: name 'b' is not defined

    print traceback.extract_tb(tb)
    # 输出(filename, line number, function name, text)
 [('1.py', 4, '', 'a = b+ c')]

    print traceback.format_exception_only(t,v)
    #输出1个list，只包括具体的exception error：
    ["NameError: name 'b' is not defined\n"]

    print traceback.format_exception(t,v,tb)
    #输出1个list，包括stack trace + exception information
['Traceback (most recent call last):\n',
'  File "1.py", line 4, in \n    a = b+ c\n',
 "NameError: name 'b' is not defined\n"]

    print  traceback.format_tb(tb)
    # A shorthand for format_list(extract_tb(tb, limit))
['  File "1.py", line 4, in \n    a = b+ c\n']

    print traceback.tb_lineno(tb)
    # returns the current line number set in the traceback object
4