Static typing [was Re: Python and the need for speed]
bc at freeuk.com
Sun Apr 16 06:55:57 EDT 2017
On 16/04/2017 05:27, Steve D'Aprano wrote:
> On Sat, 15 Apr 2017 11:55 am, Rick Johnson wrote:
>> apparently, the py-devs believe we
>> only deserve type declarations that do nothing to speed up
>> code execution (aka: type-hints), instead of type
>> declarations that could actually speed up the code. Go
>> I'm not a fan of forced static typing, but i am a fan of
>> optional static typing.
> Are you aware that optional static typing CANNOT be used for optimization?
> Since it is *optional*, it is only a hint, not a fact. You can tell the
> compiler that you believe that n will be an int, but it's not guaranteed.
No, Rick distinguished between hints, and actual declarations. It
doesn't matter if the latter are optional.
I played around with this at one time. All variables were of type
'variant', unless they had an explicit type declaration.
But it got complicated. I decided to keep the dynamic language pure, as
after all I had a statically compiled language with exactly the same
syntax if I needed it faster!
Examples A and B here: https://pastebin.com/D89zP3LF
Example C of the same silly program in Python:
for i in range(100000000):
sum += add(a,b)
a += 1
b += 2
A (Pure HLL**) 13 seconds (dynamic/interpreted)
A (With ASM module) 3
A (With ASM module) 2 (older version; hmmm...)
B (my compiler) 0.5 (static/compiled)
B (via C/gcc-O3) 0.14
C (Python 2) 163
C (Python 2/xrange) 30
C (Python 3) 38
C (Pypy) 5
(Python 2 with 'range' locked up my machine for nearly 3 minutes because
it presumably exhausted the 4GB memory just executing a simple loop.
Have I mentioned that building a massive list just to execute 'for' was
a stupid idea?)
The pypy timing is not bad, however it is misleading: you can't for
example deduce the execution time of one iteration by dividing by 100
million, as you can with the others (gcc-O3 excepted as I've no idea
what it does). You only get that timing if you actually wanted 100
> (That doesn't necessarily mean that you have to use type declarations, like
> in C, Pascal and Java. A good modern compiler can infer types, like in ML
> and Haskell.)
Yes a good, but more sophisticated, compiler. Unlike mine!
(** The pure HLL timing might be reduced to ~ 9 seconds using
'label-pointers' for dispatching, but this limited portability when
converted to C code, as not all C compilers support them. But it doesn't
matter as I can use the ASM version for speed.
I believe CPython also makes use of label-pointers when compiled with
gcc - as happens on Linux - but not when compiled with MSVC, so that
CPython on Windows is a little slower for that reason. I don't know if
this is still the case.
Those Python timings were on Windows...)
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