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 <steve@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.
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