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Re: list slice and generators

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  Re: list slice and generators Ian Kelly <ian.g.kelly@gmail.com> - 2015-11-25 10:44 -0700

#99467 — Re: list slice and generators

On Wed, Nov 25, 2015 at 3:07 AM, Peter Otten <__peter__@web.de> wrote:
> to get down to one intermediate list. Avoiding the last one is a bit tricky:
>
> metrics = (converter(x.metric(name)) for x in self._server_per_proc)
> metrics = (x for x in metrics if x is not None)
> try:
>     # if there is at least one item the generator is not empty
>     first = next(metrics)
> except StopIteration:
>     metrics = ()
> else:
>     # put the first item back in
>     metrics = itertools.chain([first], metrics)
>     assert metrics

metrics is always going to be an itertools.chain object at this
assert, so how could the assertion ever fail?

>>     elif name in METRICS_AVG:
>           # writing a function that calculates the average without
>           # materialising the list left as an exercise ;)

        metrics = itertools.tee(metrics)
        return int(sum(metrics[0]) / len(metrics[1]))

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