replacing `else` with `then` in `for` and `try`

[Jon Ribbens]

On 2017-11-03, Steve D'Aprano <steve+python at pearwood.info> wrote:
> The for loop does not necessarily perform a search:
>
> count = 1
> for obj in sequence:
>     if count > MAX_OBJECTS:
>         print("too many objects, halting")
>         break
>     process(obj)
> else:
>     print("finished")
>
> According to your mental model, this code is... what? Illegal? Silly?
> Impossible? A syntax error?

That conforms to my model. It's searching for the condition
'count > MAX_OBJECTS'.

> Even when there is a search, the sense of the search may be reversed
> from your mental model:
>
> for request in sequence:
>     if 'please' not in request:
>         break
>     process(request)
> else:
>     print('done')
>     return
> raise SysExit('failure to say please')

That's searching for the condition "'please' not in request".

> It doesn't matter if you can think of alternative ways of writing these code
> snippets. They're legal, and they work, and your mental model doesn't cover
> them, at all or easily. That means your mental model is at best incomplete.

You've yet to come up with one that it doesn't cover.

> In other words, it was only when I realised that `else` would be better
> written as `then` that I understood the behaviour of the statement. If I read
> it as "else", then the natural interpretation is that the block runs only if
> the loop doesn't run:

You're repeating yourself.

> You'll probably dismiss them as "silly" because they don't meet your mental
> model, and insist that I would be wrong to use them.

As above, you're mistaken.

> Your response to code that doesn't match your mental model is to say
> that it is obviously wrong and probably buggy and should be made
> into a syntax error if possible.

No, it isn't. Try reading again what I actually wrote.

> And my mental model is to treat "else" in this concept as some foreign word,
> perhaps Dutch, a false-friend that actually means "next" but due to some
> awful coincidence happens to look exactly like the English word for "else".

And that's leading you into confusion, as you've demonstrated.

> Ah yes, because it is inconceivable that anyone might have thought of a use
> for for...else without a break.

It's not inconceivable, but nobody has thought of a sensible use so far
(by which I mean one that shows it's a useful feature).

> What matters is that only code that matches your model is allowed.

You do seem to enjoy telling other people what their opinions are.
Frankly, I don't know why I even bother having opinions when you're
here to tell me what they are. In future, I'll just come to you to
find out what I think.

>> It's an incredibly obscure work-around for a different problem,
>
> You mean a different problem to "searching"? Yes indeed it is.

No, I mean a problem that has nothing to do with 'for...else' clauses.
If your door is stuck then you might climb in through a window, but
that doesn't mean that the purpose of windows is to be entrances,
or that windows should be designed to make them better entrances,
or that the problem isn't the stuck door.

>>> And while I thank you for the complement that I am the cleverest and most
>>> insightful Python coder in the world,
>> 
>> I didn't say anything even remotely resembling that.
>
> That was sarcasm.

Yes dear.