On 3/3/2021 2:49 PM, Irit Katriel via Python-Dev wrote:

On Wed, Mar 3, 2021 at 10:39 PM Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:
On 4/03/21 5:37 am, Paul Moore wrote:
> frameworks and libraries typically have to interact with other users'
> code, and there the contract has changed from "do what you like in
> your code and I'll cope" to "do what you like in your code as long as
> you don't let an exception group escape, and I'll cope"... And I have
> to change *my* code to get the old contract back.

Seems to me this whole issue would go away if the ordinary
except statement were to look inside ExceptionGroups.

In other words, the only difference between except and
except* would be that multiple except* clauses can be run,
whereas only one except clause will run (the first one that
matches something in the ExceptionGroup).

Is there any good reason not to do things that way?

That's an interesting idea. 

Do you mean that one exception gets handled and the rest of the group is reraised? Or discarded?

The value of sys.exc_info() (and the e in "except T as e:") needs to be a single naked exception. So if there is more than one match in the group we would need to pick one (let's say the first in DFS order).

If we do this, then we have this situation. Before ExceptionGroups, you got to choose which of the exceptions you have is the most important, and you raised only that one. Now you raise a bunch of them and the order of the except clauses in caller's code determines which one of them counts and which ones are discarded. What do you make of that?

You _could_ implement it as you said, but remember, you that with this idea, you are changing how except clauses work—so instead of making the order of the except clauses determine which one counts most, you could instead do something else.

One alternative idea would be to take the "first in DFS order" and see if it matches any of the except clauses, and if so, process that one.  If not, then pick the next, and see if it matches, until one is found that matches, and can be processed.