Re: [Python-ideas] A cute Python implementation of itertools.tee

16 Apr 2018


      On Mon, Apr 16, 2018 at 12:06 AM, Tim Peters  wrote:
...
[Koos Zevenhoven ]
...
.... It's definitely possible to write the above in a more
readable way, and FWIW I don't think it involves "assignments as
expressions".
Of course it is.  The point was brevity and speed, not readability.
It was presented partly as a puzzle :-)
...
...
What I find kind of hilarious is that it's no help at all as a
prototype for a C implementation:  Python recycles stale `[next(it),
None]` pairs all by itself, when their internal refcounts fall to 0.
That's the hardest part.
...
Why can't the C implementation use Python refcounts? Are you talking
about
standalone C code?
Yes, expressing the algorithm in plain old C, not building on top of
(say) the Python C API.
There must have been a reason why pseudo code was "invented".
...
...
Or perhaps you are thinking about overhead?
Nope.
...
(In PEP 555 that was not a concern, though). Surely it would make sense
to reuse the refcounting code that's already there. There are no cycles
here, so it's not particulaly complicated -- just duplication.
Anyway, the whole linked list is unnecessary if the iterable can be
iterated
over multiple times.
If the latter were how iterables always worked, there would be no need
for tee() at all.  It's tee's _purpose_ to make it possible for
multiple consumers to traverse an iterable's can't-restart-or-even
-go-back result sequence each at their own pace.
Yes. (I'm not sure which is easier, going back or starting from the
beginning)

-- Koos


-- 
+ Koos Zevenhoven + http://twitter.com/k7hoven +