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

[Steven D'Aprano]

On Wed, Feb 10, 2016 at 08:41:27PM -0800, Andrew Barnert wrote:

> And honestly, are you really claiming that in your opinion, "123_456_" 
> is worse than all of their other examples, like "1_23__4"?

Yes I am, because 123_456_ looks like you've forgotten to finish typing 
the last group of digits, while 1_23__4 merely looks like you have no 
taste.

> They're both presented as something the syntax allows, and neither one 
> looks like something I'd ever want to write, much less promote in a 
> style guide or something, but neither one screams out as something 
> that's so heinous we need to complicate the language to ensure it 
> raises a SyntaxError. Yes, that's my opinion, but do.you really have a 
> different opinion about any part of that?

I don't think the rule "underscores must occur between digits" is 
complicating the specification. It is *less* complicated to explain this 
rule than to give a whole lot of special cases

- can you use a leading or trailing underscore?
- can an underscore follow the base prefix 0b 0o 0x?
- can an underscore precede or follow the decimal place?
- can an underscore precede or follow a + or - sign?
- can an underscore precede or follow the e|E exponent symbol?
- can an underscore precede or follow the j suffix for complex numbers?

versus 

- underscores can only appear between (hex)digits.

I'm not sure why you seem to think that "only between digits" is more 
complex than the alternative -- to me it is less complex, with no 
special cases to memorise, just one general rule.

Of course, if (generic) you think that it is a feature to be able to put 
underscores before the decimal point, after the E exponent, etc. then 
you will dislike my suggested rule. That's okay, but in that case, it is 
not because of "simplicity|complexity" but because (generic) you want to 
be able to write things which my rule would prohibit.



-- 
Steve