On Thu, 12 Mar 2020 at 15:06, Eric Wieser <wieser.eric+nu...@gmail.com> wrote:
> will print the same id three times. However, when used as a list > comprehension, the optimization can't step in, and I have no way of using the > `del` keyword > > >>> [id(v) for v in itertools.combinations([1, 2, 3], 1)] > [2500926200992, 2500926199072, 2500926200992] You can get the same effect by not naming the value being thrown away: >>> list(map(id, itertools.combinations([1,2,3], 1))) [2267883926192, 2267883926192, 2267883926192] > `itertools.combinations` is not the only place to make this optimization - > parts of numpy use it too, allowing > > a = (b * c) + d > > to elide the temporary `b*c`. This elision can't happen with the spelling > > bc = b * c > a = bc + d > > My suggestion would be to make `del x` an expression, with semantics "unbind > the name `x`, and evaluate to its value". > This would allow: > > >>> [id(del v) for v in itertools.combinations([1, 2, 3], 1)] > [2500926200992, 2500926200992, 2500926200992] > > and > > bc = b * c > a = (del bc) + d # in C++, this would be `std::move(bc) + d` But why would you want this anyway? Do you have an example of an application where this sort of micro-optimisation is significant enough to justify a fairly major language change? (And yes, I know the optimisation in itertools could just as easily be dismissed as "why is this needed?", but that didn't need a language change to implement...) Paul _______________________________________________ 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/QVXZI5KCBORHXOT4KR2SGLASFXCIXFVF/ Code of Conduct: http://python.org/psf/codeofconduct/
