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Raising an exception in the caller's frame

logistix logistix at zworg.com
Fri Mar 21 15:16:49 EST 2003 
Thomas Heller <theller at python.net> wrote in message news:<7kas50ex.fsf at python.net>...
> Alex Martelli <aleax at aleax.it> writes:
> 
> > Thomas Heller wrote:
> >    ...
> > > Hopefully I can explain it: check_result() is not the 'cause' of the
> > > error, it's purpose is simply to detect the error. The 'exception'
> > > really occurrs in dosomething().
> > 
> > Yes, your purpose is very clear to me and I agree there _should_
> > be a way to achieve it, but I can't think of one.
> > 
> > 
> 
> The best I came up with so far is to *return* an exception
> instead of raising it, and do a typecheck in the caller:
> 
> def check_result(value):
>     if somecondition(value):
>         return ValueError(value) # or whatever
>     return value
> 
> def do_some_work():
>     value = dosomething()
>     result = check_result(value)
>     if isinstance(result, Exception):
>         raise result
>     return result
> 
> Thomas

Aren't you just really trying to assert?

def do_some_work():
    value = dosomething()
    assert somecondition(value), "Failed somecondition test!"
    return value
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