Reraise exception with modified stack

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
.

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