On 13/03/2016 20:57, Chris Angelico wrote:
On Mon, Mar 14, 2016 at 6:39 AM, BartC <b...@freeuk.com> wrote:
I used it in my benchmark to replace the if-else chain checking three lots
of ranges:
switch(c)
if case(ord("A"),ord("B"),ord("C"),ord("D"),ord("E"),ord("F"),
It worked, but took 110 seconds; 80 seconds without the ord's and comparing
strings (but I still think it's perverse that integer ops are slower than
string ops).
But 110 or 80 seconds, the original Python was 3.6 seconds. (Probably,
someone could tweak it to work with ranges, but this is extra programmer
effort that you say is too valuable to waste on such matters.)
This is not comparing ranges, though. This is comparing against
individual values.
That's true. (It's not my code for 'switch' and 'case', and I assume
that the "==" operation it does on the arguments would not work when a
range is passed, whatever form that might be in.)
Nevertheless, a true switch statement would be expected to work just as
well with lots of individual case values, as with a smaller set of ranges.
To talk about comparing ranges, I would expect the
code to look something like this:
switch(c)
if case("A", "Z"):
upper += 1
elif case("a", "z"):
lower += 1
elif case("0", "9"):
digits += 1
else:
other += 1
THIS is comparing ranges.
The underlying comparisons must be
inequalities, not equalities. I absolutely *do not care* about
performance until the code looks good - at least reasonably good.
Yes, that would be faster. I made a much-simplified case() work like
your example, and the timing was 12 seconds.
(But that just worked with one single range, not an arbitrary mix of
single values and ranges as a proper switch. Allowing any number of
ranges per case, it took 25 seconds, and it's still not quite a full
switch.)
(By the way, your switch/case pair is non-reentrant. Plus it uses a
class in a weird way. Why not, if you're working like this, just have
two functions and a module-global? Just as non-reentrant, much cleaner
code.)
I chose this because it looked odd, and was likely to perform poorly!
My point being that it's difficult to put together something that looks
like, and is as easy to use as a switch in other languages, and is still
efficient. (The 12 seconds still took over 3 times as long as as a
simple if-elif chain, and the tests are still sequential so expect a
slow-down with lots groups to test.)
--
Bartc
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