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Being able to break multiple loops and having "labelled" breaks would be achievable using `except`, i.e. adding `except` to the loop statements before `else` like this: for elem in iterable:
... if should_break(elem): raise SomeException except SomeException as e: handle_break_behaviour(e) else: print("Did not break")
would be sugar for: try:
for elem in iterable: ... if should_break(elem): raise SomeException except SomeException as e: handle_break_behaviour(e) else: print("Did not break")
I (and others) have suggested this before and no one has said it's a *bad *option, it's just been ignored, despite seeming to be an intuitive way to accomplish `else` clarity, "labelled" breaks and breaking from multiple loops. Is there a reason that this suggestion is worse / no better than adding special break syntax? As for an example for labelled breaks how about something of the form: def insert_ordered_no_duplicates(duplicate_free_list, item):
for i, elem in enumerate(duplicate_free_list): if elem == item: break already_present if elem > item: break location_found case already_present: return duplicate_free_list case location_found: new_list = duplicate_free_list[:] new_list.insert(i, item) return new_list new_list = duplicate_free_list[:] new_list.append(item) return new_list
which you can conceivably have a nested case where you don't want to let duplicate inserts even be attempted like this: def insert_many_ordered_strictly_no_duplicates(dup_free_list, items):
new_list = dup_free_list[:] for item in items: for i, elem in new_list: if elem == item: break already_present if elem > item: break location_found case already_present: break duplicates_attempted case location_found: new_list.insert(i, item) else: new_list.append(item) case duplicates_attempted: return dup_free_list[:] return new_list
On Wed, 5 Aug 2020 at 13:40, Rob Cliffe via Python-ideas < python-ideas@python.org> wrote:
I note that both of these examples could be handled by having a way to break out of 2 loops at a time. Rob
On 29/07/2020 12:33, Jonathan Fine wrote:
Thank you all, particularly Guido, for your contributions. Having some examples will help support the exploration of this idea.
Here's a baby example - searching in a nested loop. Suppose we're looking for the word 'apple' in a collection of books. Once we've found it, we stop.
for book in books: for page in book: if 'apple' in page: break if break: break
However, suppose we say that we only look at the first 5000 or so words in each book. (We suppose a page is a list of words.)
This leads to the following code.
for book in books: word_count = 0 for page in book: word_count += len(page) if word in page: break if word_count >= 5000: break found if break found: break
At this time, I'd like us to focus on examples of existing code, and semantics that might be helpful. I think once we have this, the discussion of syntax will be easier.
By the way, the word_count example is as I typed it, but it has a typo. Did you spot it when you read it? (I only noticed it when re-reading my message.)
Finally, thank you for your contributions. More examples please.
-- Jonathan
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