could itertools.cycle not make a copy of the iterable ?
Hi everyone, first I'm not quite sure if this is the right place to make this kind of suggestion/ask question but, `itertools.cycle` makes a copy of the iterable its given and as the note says: this may require significant auxiliary storage. Maybe I don't see the reason why this is nescessary but, shouldn't this work just as well: ``` def cycle(iterable): # cycle('ABCD') --> A B C D A B C D A B C D ... while iterable: for element in iterable: yield element ``` Instead of the current: ``` def cycle(iterable): # cycle('ABCD') --> A B C D A B C D A B C D ... saved = [] for element in iterable: yield element saved.append(element) while saved: for element in saved: yield element ```
On Wed, Jan 19, 2022 at 10:49 AM jerome via code-quality < code-quality@python.org> wrote:
Hi everyone, first I'm not quite sure if this is the right place to make this kind of suggestion/ask question but, `itertools.cycle` makes a copy of the iterable its given and as the note says: this may require significant auxiliary storage. Maybe I don't see the reason why this is nescessary but, shouldn't this work just as well:
This definitely isn't the right place, but I'll give you something to think about to help answer your question anyway.
``` def cycle(iterable): # cycle('ABCD') --> A B C D A B C D A B C D ... while iterable: for element in iterable: yield element ```
Let's say I give you an iterable that looks like: ``` import random import typing def generate_random(limit: int = 5) -> typing.Generator[int, None, None]: for _ in range(limit): yield random.randint(0, 1_000_000) cycle(generate_random()) ``` How would your your revised version behave? How does that compare to the stdlib version? Instead of the current:
``` def cycle(iterable): # cycle('ABCD') --> A B C D A B C D A B C D ... saved = [] for element in iterable: yield element saved.append(element) while saved: for element in saved: yield element ``` _______________________________________________ code-quality mailing list -- code-quality@python.org To unsubscribe send an email to code-quality-leave@python.org https://mail.python.org/mailman3/lists/code-quality.python.org/ Member address: graffatcolmingov@gmail.com
Thank you for the answer, yes I now see where the problem is. My reasoning was that in those case the responsibily should fall upon the user to make a list first instead of making a copy each time, but now I see that it can wait for ever in some cases. Sorry for posting in the wrong place !
If you use a generator instead of a string then you'll only loop once and wait forever. On Wed, Jan 19, 2022 at 11:49 AM jerome via code-quality < code-quality@python.org> wrote:
Hi everyone, first I'm not quite sure if this is the right place to make this kind of suggestion/ask question but, `itertools.cycle` makes a copy of the iterable its given and as the note says: this may require significant auxiliary storage. Maybe I don't see the reason why this is nescessary but, shouldn't this work just as well: ``` def cycle(iterable): # cycle('ABCD') --> A B C D A B C D A B C D ... while iterable: for element in iterable: yield element ``` Instead of the current:
``` def cycle(iterable): # cycle('ABCD') --> A B C D A B C D A B C D ... saved = [] for element in iterable: yield element saved.append(element) while saved: for element in saved: yield element ``` _______________________________________________ code-quality mailing list -- code-quality@python.org To unsubscribe send an email to code-quality-leave@python.org https://mail.python.org/mailman3/lists/code-quality.python.org/ Member address: dstanek@dstanek.com
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Thank for the answer David, waiting forever is indeed a problem. It seems obvious now .
participants (4)
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David Stanek -
Ian Stapleton Cordasco -
jerome.guay＠protonmail.com -
Jérôme Guay