[Python-ideas] Star assignment in iterator way?
steve at pearwood.info
Tue Nov 21 05:53:38 EST 2017
On Tue, Nov 21, 2017 at 12:27:32PM +0300, Kirill Balunov wrote:
> Backward compatibility is an important issue, but at the same time it is
> the main brake on progress.
"Progress just means bad things happen faster."
-- Terry Pratchett, "Witches Abroad"
> And how do you look at something like this (deferred star evaluation)?:
> a, ?*b, c, d = something_iterable
A waste of effort?
How do you defer evaluating the second and subsequent items if you
evaluate the final two? Given:
for i in range(100):
a, ?*b, c, d = gen()
has to evaluate all 100 random numbers in order to assign a, c, d all
equal to 999. Making b an iterator instead of a list doesn't actually
avoid evaluating anything, and it will still require as much storage as
a list. The most likely implementation would:
- store the evaluated items in a list;
- assign iter(the list) as b.
I suppose that there could be some way of delaying the calls to
random.random() by returning a thunk, but that is likely to be more
expensive in both memory and time than a simple list of floats.
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