Constants [was Re: newb question about @property]

[Steve D'Aprano]

On Thu, 5 Oct 2017 12:41 am, Ian Kelly wrote:

> Python has the simplest named constants of all:
> 
> C = 12345
> 
> As long as you don't subsequently change it, it's a constant. And it's
> very simple because it works just like any other variable.


I do feel that the lack of constants[1] is a (mild) weakness of Python. In
small projects, if you want a constant:

pi = 3.1415

and you don't want to change it, it is easy enough to remember to just not
change it. Especially if you follow a naming convention like using ALLCAPS
for constants.

But in large projects, especially those where you cannot trust every module in
the project to obey the naming convention, I can see that this lack might
contribute to the perception, if not the fact, of Python being a bit too
unsafe for big projects. We have read-only attributes in classes, but not
read-only names in modules. That makes me a little bit sad.

Back in the day when I used Pascal regularly, I recall having the compiler
complain when I accidentally tried to assign a new value to a constant. But I
was a much less experienced coder back then. In all honesty, I can't remember
the last time I accidentally reassigned to something intended as a constant.

Nevertheless, constants are a safety net I would appreciate.




[1] By which I mean names which can only be bound once, but not rebound. This
is not about mutability, it is about whether or not the name can be rebound.


-- 
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.