On Thu, Aug 10, 2017 at 8:39 AM, Paul Moore <p.f.mo...@gmail.com> wrote:
> Also, there's a potential issue > here - consider > > [expr for var in even_numbers() if is_odd(var) while var < 100] > > This is an infinite loop, even though it has a finite termination > condition (var < 100), because we only test the termination condition > if var is odd, which it never will be. > why is the termination only tested if teh if clause is True? Could then not be processed in parallel? or the while first.... so maybe better to do: [expr for var in even_numbers() while var < 100 if is_odd(var)] Maybe it's just me, but I would certainly expect the while to have precedence. I guess I think of it like this: "if" is providing a filtering mechanism "while" is providing a termination mechanism -- is there a use case anyone can think of when they would want the while to be applied to the list AFTER filtering? Obviously, this is a contrived example. And certainly "don't do that, > then" is a valid response. But my instinct is that people are going to > get this wrong - *especially* in a maintenance environment. sure, but would there be an issue if teh while were given precedence? Overall, I agree with Steven's point. It seems pretty obvious what the > intention is, and while it's probably possible to construct examples > that are somewhat unclear, > > 1. The mechanical rule gives an explicit meaning > 2. People shouldn't be writing such complex comprehensions, so if the > rule doesn't give what they expect, they can always rewrite the code > with an explicit (and clearer) loop. > me too -- a direct translation to a for loop isn't necessary to understand how it works. -CHB -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov
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