[Python-Dev] with_traceback

[Greg Ewing]

Adam Olsen wrote:

> Exceptions aren't arbitrary objects though.  The requirement that they
> inherit from BaseException is specifically to create a common
> interface.

But that doesn't tell you enough. If the exception
references some other object, should you copy it?
You can't tell just from the fact that it inherits
from BaseException.

Besides, making a copy of the exception seems just
as expensive as creating a new instance, so it does
nothing to address the efficiency issue.

Maybe it's not as important as I feel it is, but I
like the way that exception raising is lightweight
enough to use for flow control. When used that way,
creating a new instance each time seems wasteful.
I accept the overhead because I know that if it were
ever a problem I could eliminate it by pre-creating
the instance. I'd be disappointed to lose that
ability.

> I believe calling copy.copy() would be sufficient.

I never use that, because I have no confidence that
it would DWIM. I'd be unhappy if the system started
relying on it anywhere fundamental.

-- 
Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | Carpe post meridiem!          	  |
Christchurch, New Zealand	   | (I'm not a morning person.)          |
greg.ewing at canterbury.ac.nz	   +--------------------------------------+