[Python-ideas] Allow using symbols from Unicode block "Superscripts and Subscripts" in identifiers

[Steven D'Aprano]

On Fri, May 02, 2014 at 10:27:56PM -0400, Terry Reedy wrote:

> If the rules for identifiers are expanded, any code the uses newly 
> allowed names cannot be backported or run on previous versions. In 
> contracted, the opposite problem occurs. I do not think they should be 
> changed either way without a strong cause.

That applies to any new feature -- code using that feature cannot be 
easily backported. In this case, it's actually quite simple to backport 
code using the new rules for identifiers: just change the identifiers. 
The algorithm used by the code remains that same.


> > From 2.3. Identifiers and keywords
> >"The syntax of identifiers in Python is based on the Unicode standard
> >annex UAX-31, with elaboration and changes as defined below; see also
> >PEP 3131 for further details."
> 
> In other words, we use the standard with a few intentional 
> modifications.  

Playing Devil's Advocate, perhaps we could add a few more intentional 
modifications.

While there are advantages to following a standard just for the sake of 
following a standard, once you allow any changes, you're no longer 
following the standard. So the argument becomes, why should we allow 
that change but not this change?

Particularly for mathematically-focused code, I think it would be useful 
to be able to use identifiers like (say) σ² for variance, g₁ for sample 
skewness, or β₂ for Pearson's skewness, to give a few real-world 
examples. Regular digits may be ambiguous: compare s₁² for the sample 
variance with Bessel's correction, versus s12. (s twelve?)

I'm going to give a tentative +1 vote to allowing superscript and 
subscript letters and digits in identifiers, if it can be done without 
excessive cost in complexity or performance. Anything else, like (say) ⑤ 
(CIRCLED DIGIT FIVE), I will give a firm -1.



-- 
Steven