Python and the need for speed

bartc bc at freeuk.com
Sat Apr 15 08:17:45 EDT 2017


On 15/04/2017 03:35, Rick Johnson wrote:
> On Wednesday, April 12, 2017 at 8:44:30 AM UTC-5, bart... at gmail.com wrote:

> At a minimum, every language should offer
> the following four loop-forms (using Python semantics):
>
>     while CONDITION:
>         doSomething()
>
>     for VALUE in COLLECTION:
>         doSomething(value)
>
>     loop(N):
>         doSomething()
>
>     loop(N) as i:
>        doSomething(i)
>

Yes, I'm constantly surprised at this, as such syntax has a very low 
cost (in my last compiler, supporting 'while' for example only added 30 
lines to the project).

Of course, it's possible to overdo it; if you look at Lisp, you'll lose 
yourself in the myriad looping options.

But very common requirements are endless loops, and repeat N times 
without needing an explicit counter. The former /can/ be easily written as:

     while 1:
         body

but it's more psychological; I don't want to use an idiom to denote an 
endless loop, I want to be able to express it directly!

Python's byte-code does at least optimise out the check that '1' is 
true, but that's not what the reader sees, which is 'loop while 1 is 
true'. And one day it will be:

     while l:
         body

that can be mistaken for that common idiom.

-- 
bartc


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