On 15/03/2016 00:28, Mark Lawrence wrote:
On 14/03/2016 23:56, BartC wrote:
Anything so terrible about that that Python needs to keep well clear of
or that you think its users should be deprived of?
Yes, it is not even valid Python. Switch has been rejected via at least
one PEP and from what I see it adds nothing to the language, so let's
deprive it from people who clearly don't need it in the first place.
Every time you need to test X against more than one other value, then
you have a potential use for switch.
But yes you can do without switch if you have too. Same for many features.
I am only rude to people such as yourself who refuse to provide code, in
fact anything, to support your case. Your "benchmark" for the switch
was yet another laughable farce, which only tested the function calls,
building tuples, running loops, there was nothing to test with respect
to the actual switch which was meant to be tested. So just in case you
missed it above, where is the profile for this test?
I've shown the task. I'm sure you can also do some tests and show us
some results.
I agree with you. But once you've got the language right, then there's
no harm looking at performance. A switch statement like the above can be
executed in a single byte-code.
Really? Then please show us all just how it can be done via a patch to
the cPython code on the bug tracker.
The one-byte-code switch works when all case expressions are known at
compile-time. It makes use of a jump-table within the byte-code.
The total sequence will be more than one byte-code, typically:
LOAD_FAST The index
SWITCH Jump to the right label
....
L5: One of multiple labels
... Deal with the code in this branch
JUMP_ABSOLUTE Break out of the switch
... Provision is needed for the jump-table
But only one is needed for testing and dispatch. Now I've sketched it
out, perhaps you can fill in the details for yourself... (I'm not
getting involved in CPython development.)
--
Bartc
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