[Python-ideas] Delayed Execution via Keyword

Ed Kellett edk141 at gmail.com
Fri Feb 17 16:14:29 EST 2017

On Fri, 17 Feb 2017 at 19:38 Joseph Jevnik <joejev at gmail.com> wrote:

> Delayed execution and respecting mutable semantics seems like a nightmare.
> For most indexers we assume hashability which implies immutability, why
> can't we also do that here? Also, why do we need to evaluate callables
> eagerly?

Respecting mutability: we just have to always, we don't know if a delayed
thing is hashable until we evaluate it. This thing has implications for
existing code (since delayed objects can get anywhere) so it should be
careful not to do anything too unpredictable, and I think d[k] meaning
"whatever is in d[k] in five minutes' time" is unpredictable. One can
always delay: d[k] if it's wanted.

Evaluate calls: because if you don't, there's no way to say "strictly
evaluate x() for its side effects".
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