The point is that `for-else` reads like "do this for loop ELSE (or but if
you can't loop) do this", i.e. roughly equivalent to this:
> try:
> loop_entered = False
> for loop_entered, elem in enumerate(iterable, start=1):
> pass
> assert loop_entered
> except AssertionError:
> print("loop not entered")
>
or
> loop_entered = False
> for loop_entered, elem in enumerate(iterable, start=1):
> pass
> if loop_entered:
> pass
> else:
> print("loop not entered")
>
But that isn't what it means. It means "do this for loop and if you
deliberately break out, continue ELSE (or if you don't break out) do this".
i.e. roughly equivalent to this:
> loop_broken = False
> for elem in iterable:
> if should_break(elem):
> loop_broken = True
> break
> if not loop_broken:
> print("you didn't break from the loop you maybe entered...")
>
or
> loop_broken = False
> for elem in iterable:
> if should_break(elem):
> loop_broken = True
> break
> if loop_broken:
>
pass
>
else:
>
print("you didn't break from the loop you maybe entered...")
>
which is not intuitive because `else` reads like it handles the unexpected
case, which one would have guessed was either breaking out or not entering
in the first place.
On Wed, 15 Jul 2020 at 09:23, Dominik Vilsmeier <dominik.vilsme...@gmx.de>
wrote:
> But `finally` with a `for` loop is redundant since the code can be placed
> just after the loop. For `try/except` it's a different situation since the
> exception might bubble up, so "normal" code after the `try` won't be
> reached.
>
> Also `on_break` doesn't seem really important since that code can be
> executed inside the loop right before the `break`.
>
> We already have `else` for `on_finish` and I think when recalling the
> analogy to exceptions it's not that confusing: a `try` block can be exited
> either normally (because all code has been executed) or because it raised
> an exception; here `else` means it exited normally. Similarly a `for` loop
> can terminate either normally by executing all iterations or because a
> `break` occurred; and similarly `else` means it terminated normally.
> On 15.07.20 08:47, Mathew Elman wrote:
>
> But in `for...else` the `else` call isn't always called, so changing
> `else` for `finally` doesn't make sense. What you're suggesting is
> replacing `else` with `on_finish` and adding `finally` and `on_break`.
>
> I agree that having `finally` could make the use cases of `else` clearer,
> but I am not convinced renaming "else" to "on_finish" would help the
> confusion for the 0 iteration case.
>
> I think that since this suggestion doesn't help with the 0 iteration case
> (my first idea here didn't either), it feels like added extra compound
> statements need to be immediately intuitive to be worth having - either
> because they read like a sentence or parallel existing python e.g.
> `try-except-else-finally` or `if-elif-else` etc.
>
>
> On Wed, 15 Jul 2020 at 06:47, Steve Barnes <gadgetst...@live.co.uk> wrote:
>
>> Can I suggest that for loops the `else` would be a lot clearer if it was
>> spelt `finally` as was done for PEP-0341 for try blocks and that we
>> might possibly need one or more `on_…` clauses such as `on_break` and `
>> on_finish` I think that this would be a lot clearer:
>>
>>
>>
>> for i in range(N):
>>
>> if i > 3:
>>
>> break;
>>
>> on_break: # Called if loop was broken
>>
>> print(i)
>>
>> on_finish: # Called if loop was not broken
>>
>> print("Loop Completed")
>>
>> finally: # Always called (replaces for…else)
>>
>> print("Loop Ended")
>>
>>
>>
>> Which I think would be a lot easier for newcomers to learn than
>> try…for…else…except…else e.g.:
>>
>>
>>
>> try:
>>
>> for i in range(N):
>>
>> if i > 3:
>>
>> break;
>>
>> elif i % 2 == 0:
>>
>> raise ValueError("Odds Only");
>>
>> else: # to if
>>
>> print(i)
>>
>> else: # Else to loop
>>
>> print("Loop Completed")
>>
>> except ValueError as err:
>>
>> print(err)
>>
>> else: # to try
>>
>> print("No Exception")
>>
>> finally:
>>
>> print("Try Ended")
>>
>>
>>
>> Where the multitude of elses makes my eyes cross.
>>
>>
>>
>> Steve Barnes
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