It seems like this is all an occasion to use itertools.tee() ... But with a consciousness that implicit caching uses memory.
On Mon, Jun 20, 2022, 11:36 PM Steven D'Aprano <st...@pearwood.info> wrote: > On Sun, Jun 19, 2022 at 01:34:35AM +0100, Rob Cliffe via Python-ideas > wrote: > > > To me, the natural implementation of slicing on a non-reusable iterator > > (such as a generator) would be that you are not allowed to go backwards > > or even stand still: > > mygen[42] > > mygen[42] > > ValueError: Element 42 of iterator has already been used > > How does a generic iterator, including generators, know whether or not > item 42 has already been seen? > > islice for generators is really just a thin wrapper around an iterator > that operates something vaguely like this: > > for i in range(start): > next(iterator) # throw the result away > for i in range(start, end): > yield next(iterator) > > It doesn't need to keep track of the last index seen, it just blindly > advances through the iterator, with some short-cuts for the sake of > efficiency. > > > -- > Steve > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/A74YRQJ4QID72GE5I2A3QKOU6NHLJNCD/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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