[Python-Dev] PEP 515: Underscores in Numeric Literals

[Steven D'Aprano]

On Thu, Feb 11, 2016 at 08:50:09PM +0200, Serhiy Storchaka wrote:

> I have strong preference for more strict and simpler rule, used by most 
> other languages -- "only between two digits". Main arguments:
> 
> 1. Simple rule is easier to understand, remember and recognize. I care 
> not about the complexity of the implementation (there is no large 
> difference), but about cognitive complexity.
> 
> 2. Most languages use this rule. It is better to follow non-formal 
> standard that invent the rule that differs from rules in every other 
> language. This will help programmers that use multiple languages.
> 
> I have provided an alternative patch and can provide an alternative PEP 
> if it is needed.

I don't think an alternative PEP is needed, but I hope that your 
alternative gets a fair treatment in the PEP.


> >The production list for integer literals would therefore look like this::
> >
> >    integer: decimalinteger | octinteger | hexinteger | bininteger
> >    decimalinteger: nonzerodigit (digit | "_")* | "0" ("0" | "_")*
> >    nonzerodigit: "1"..."9"
> >    digit: "0"..."9"
> >    octinteger: "0" ("o" | "O") "_"* octdigit (octdigit | "_")*
> 
>      octinteger: "0" ("o" | "O") octdigit (["_"] octdigit)*
> 
> >    hexinteger: "0" ("x" | "X") "_"* hexdigit (hexdigit | "_")*
> 
>      hexinteger: "0" ("x" | "X") hexdigit (["_"] hexdigit)*
> 
> >    bininteger: "0" ("b" | "B") "_"* bindigit (bindigit | "_")*
> 
>      bininteger: "0" ("b" | "B") bindigit (["_"] bindigit)*

To me, Serhiy's versions (starting with single > symbols) are not only 
simpler to learn, but have a simpler (or at least shorter) 
implementation too.


[...] 
> >**Group 3: only between digits, only one underscore**
> >
> >* Ada [8]_
> >* Julia (but not in the exponent part of floats) [9]_
> >* Ruby (docs say "anywhere", in reality only between digits) [10]_
> 
> This classification is misleading. The difference between groups 2 and 3 
> is less then between different languages in group 1. To be fair, groups 
> 2 and 3 should be united in one group. C++ should be included in this 
> group. Perl 5 and Swift should be either included in both groups or 
> excluded from any group, because they have inconsistencies between the 
> documentation and the implementation or between different parts of the 
> documentation.
> 
> With correct classification it is obvious what variant is the most popular.

It is not obvious to me what you think the correct classification is.

If you disagree with Georg's classification, would you reclassify the 
languages, and if there is agreement that you are correct, he can update 
the PEP?




-- 
Steve