> Date: Wed, 8 Jul 2020 20:00:44 +0300
> From: Paul Sokolovsky <pmis...@gmail.com>
> Subject: [Python-Dev] Re: Python is the only language with lack of
[ munch ]
> Right. So, if someone would like to add something to this thread, I'd
> humbly suggest to concentrate on the lack of, and need for, of
> const-ness in the Python language core (in comparison to other languages
> or not), and usecases it enables, and not on criteria for "popularness".
>
My view is that the informal Python "don't mess with anything all in
upper case" coding convention works at least as well as any more
formal language notation for nearly all cases. It conveys intention
very well with minimum effort, and does not require programmers
to think about the language they're using rather than the problem
they are trying to solve.
I can see the case for a const annotation/keyword for simple
scalar values, almost always numbers, but am dubious about
the benefits. If someone really wants to write
IMPORTANT_SIN30 = math.sin(45)
there's only so much a compiler/interpreter can do to stop them.
"If we just provide enough detail we can catch every error" is
a mirage that's lured away so much effort for many decades.
(That said, I'd be in favour of adding math.PI and similar
names because even I find it slightly disturbing that I can write
math.pi = 3.0
and it doesn't look wrong.)
Even for simple numbers, constness can be argued. Is the
value determined when the code is written, or when run?
A lot of mutable variables in Pascal/C/Ada programs are really
constants, but the value is "number of CPU cores" or something
else that can't be determined until first use. So those other
languages that supposedly have constness are actually often
more like Python.
Once you go beyond scalar values, it's just a mess. If I write
const myd = { "answer" : 42 }
do I mean that myd will always be a reference to that object,
or that the object being pointed to has constant members?
To see what can happen if you try and build this into the
language, look at C++. It has the const keyword for objects
and object references. But then the "mutable" keyword got
added to describe object members, because programmers
needed to be able to modify the internal values of "const"
objects! So now "const" in C++ for objects just means you
don't intend to change the internal state, but it might do
so anyway.
Again, I can see a case in embedded systems for "const"
meaning "this can be put in ROM". But I don't think that
use case is common enough to justify adding to the core
language.
--
cheers,
Hugh Fisher
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