Re: Feature Suggestion: "repeat" statement in loops

On Thu, Jan 26, 2023 at 08:34:04PM +0100, Thomas Ratzke wrote:

> Hi all,
>=20
> i would like to suggest the following Python feature. It naturally=20
> happens that one want's to repeat the current iteration of a for loop=20
> for example after an error happened.

Can you give an example of when you would do that?


> For this purpose, I usually set a=20
> flag and put a while loop inside my for loop. A simple "repeat"=20
> statement just like "continue" or "break" would make the code much more=20
> readable.

Is the idea that it just restarts the current iteration, or that we=20
rewind the program state (as in reversible debugging)?

The later would be very difficult.

I think this is an interesting concept, but I fear that it would be an=20
attractive nuisance that ends up causing lots of infinite loops. If an=20
error occurs during one iteration, or some other condition, and you=20
re-run that iteration, surely the condition will continue to hold and=20
you will re-run it again, leading to an infinite loop?

Unless the error is stochastic (e.g. depends on randomness, or=20
environmental conditions which may change from one loop iteration to the=20
next) repeating the loop won't change the conditions that cause the=20
error. So I see that a `repeat` keyword would make it easy to turn a=20
nice clear exception into an annoying infinite loop.

Your sketch of an example shows the problem:

> for _ in range(n):
> =A0=A0=A0 ...
> =A0=A0=A0 if not A:
> =A0=A0=A0 =A0=A0=A0 repeat # repeat current iteration

Without changing the value of `A`, re-running the current iteration will=20
just hit the `repeat` statement again and again and again, forever.


--=20
Steve