Reraise exception with modified stack

[Nicolas Fleury]

Hi,
I've made a small utility to re-raise an exception with the same stack 
as before with additional information in it.  Since I want to keep the 
same exception type and that some types have very specific constructors 
(which take, for example, more than one parameter), the only safe way I 
have found to made it is by hacking the str representation:


import sys

class ExceptionStr:
     def __init__(self, content):
         self.content = content
         self.infos = []
     def addinfo(self, info):
         self.infos.insert(0, info)
     def __call__(self):
         return '\n' + '\n'.join(self.infos + [self.content])

def reraise(exception, additionalInfo):
     strFunc = getattr(exception, "__str__", None)
     if not isinstance(strFunc, ExceptionStr):
         strFunc = ExceptionStr(str(exception))
         exception.__str__ = strFunc
     strFunc.addinfo(additionalInfo)
     raise exception, None, sys.exc_info()[-1]

if __name__ == '__main__':
     def foo():
         raise AttributeError('Test')
     def bar():
         foo()
     try:
         try:
             try:
                 bar()
             except Exception, exception:
                 reraise(exception, "While doing x:")
         except Exception, exception:
             reraise(exception, "While doing y:")
     except Exception, exception:
         reraise(exception, "While doing z:")


Suppose the resulted traceback is:

Traceback (most recent call last):
   File "somefile.py", line 52, in ?
     reraise(exception, "While doing z:", MyException)
   File "somefile.py", line 50, in ?
     reraise(exception, "While doing y:", Exception)
   File "somefile.py", line 48, in ?
     reraise(exception, "While doing x:")
   File "somefile.py", line 46, in ?
     bar()
   File "somefile.py", line 40, in bar
     foo()
   File "somefile.py", line 38, in foo
     raise AttributeError('Test')
AttributeError:
While doing z:
While doing y:
While doing x:
Test

I would like to know how to code the reraise function so that the lines 
48, 50 and 52 don't appear in the stack.  Is it possible?

Thx and regards,
Nicolas