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From: Marko Rauhamaa <marko@pacujo.net>
Newsgroups: comp.lang.python
Subject: Re: The Cost of Dynamism (was Re: Pyhon 2.x or 3.x, which is faster?)
Date: Tue, 22 Mar 2016 09:24:33 +0200
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Steven D'Aprano <steve+comp.lang.python@pearwood.info>:

> I applaud you writing different versions of code to try different
> tactics, but you should start from "write the most natural Python code
> you can" *before* you trying guessing what's fast and what's slow.

I'm hard-pressed to imagine a situation where I would write *unnatural*
Python code for performance gains. Choosing a good algorithm applies to
Python programming as well, but convoluted optimization tricks, hardly.

> On Tuesday 22 March 2016 11:49, BartC wrote:
>> No, it passes only a reference to the entire string.
>
> In Python terms, that *is* "the entire string".
>
> The point is, under the hood of the interpreter, *everything* passes
> along references. We rarely draw attention to this fact. Given:
>
> function(1.5, [])
>
> we say "pass the float 1.5 and an empty list to function", not "pass a
> reference to the float 1.5 and a reference to an empty list to a
> reference to the function", because that would get rather annoying
> quickly.

Hm. Annoying to repeat, sure, but I don't know how you could extricate
pointers from Python's abstract data model (or Java's, or Lisp's).
Prolog or a purely functional programming language could get away
without pointers but not Python.

> But that's the critical point: it is *behind the scenes*, an
> implementation detail.

I don't think there is any way to implement, think about or define
Python without pointers.

> In Python code, you don't pass "a reference to" 1.5, you pass 1.5.
> Likewise for all other objects. The abstraction is that you pass
> objects around, not references to objects.

The devil is in the mutables...


Marko