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

[Georg Brandl]

On 02/10/2016 11:35 PM, Brett Cannon wrote:

>>     Examples::
>> 
>>         # grouping decimal numbers by thousands
>>         amount = 10_000_000.0
>> 
>>         # grouping hexadecimal addresses by words
>>         addr = 0xDEAD_BEEF
>> 
>>         # grouping bits into bytes in a binary literal
>>         flags = 0b_0011_1111_0100_1110
>> 
> 
> I assume all of these examples are possible in either the liberal or restrictive
> approaches?

The last one isn't for restrictive -- its first underscore isn't between digits.

>> 
>>     Implementation
>>     ==============
>> 
>>     A preliminary patch that implements the specification given above has been
>>     posted to the issue tracker. [11]_
>> 
> 
> Is the implementation made easier or harder if we went with the Group 2 or 3
> approaches? Are there any reasonable examples that the Group 1 approach allows
> that Group 3 doesn't that people have used in other languages?

Group 3 is probably a little more work than group 2, since you have to make sure
only one consecutive underscore is present.  I don't see a point to that.

> I'm +1 on the idea, but which approach I prefer is going to be partially
> dependent on the difficulty of implementing (else I say Group 3 to make it
> easier to explain the rules).

Based on the feedback so far, I have an easier rule in mind that I will base
the next PEP revision on.  It's basically

"One ore more underscores allowed anywhere after a digit or a base specifier."

This preserves my preferred non-restrictive cases (0b_1111_0000, 1.5_j) and
disallows more controversial versions like "1.5e_+_2".

cheers,
Georg