[Python-Dev] PEP 515: Underscores in Numeric Literals (original) (raw)

Steven D'Aprano steve at pearwood.info
Thu Feb 11 19:16:34 EST 2016

On Thu, Feb 11, 2016 at 06:03:34PM +0000, Brett Cannon wrote:

On Thu, 11 Feb 2016 at 02:13 Steven D'Aprano <steve at pearwood.info> wrote:

> On Wed, Feb 10, 2016 at 08:41:27PM -0800, Andrew Barnert wrote: > > > And honestly, are you really claiming that in your opinion, "123456" > > is worse than all of their other examples, like "123_4"? > > Yes I am, because 123456 looks like you've forgotten to finish typing > the last group of digits, while 123_4 merely looks like you have no > taste. > OK, but the keyword in your sentence is "taste".

I disagree. The key idea in my sentence is that the trailing underscore looks like a programming error. In my opinion, avoiding that impression is important enough to make trailing underscores a syntax error.

I've seen a few people vote +1 for things like 123_j and 1.23_e99, but I haven't seen anyone in favour of trailing underscores. Does anyone think there is a good case for allowing trailing underscores?

If we update PEP 8 for our needs to say "Numerical literals should not have multiple underscores in a row or have a trailing underscore" then this is taken care of. We get a dead-simple rule for when underscores can be used, the implementation is simple, and we get to have more tasteful usage in the stdlib w/o forcing our tastes upon everyone or complicating the rules or implementation.

I think this is a misrepresentation of the alternative. As I see it, we have two alternatives:

To describe the second alternative as "complicating the rules" is, I think, grossly unfair. And if Serhiy's proposal is correct, the implementation is also no more complicated:

underscores after digits

octinteger: "0" ("o" | "O") ""* octdigit (octdigit | "")* hexinteger: "0" ("x" | "X") ""* hexdigit (hexdigit | "")* bininteger: "0" ("b" | "B") ""* bindigit (bindigit | "")*

underscores between digits

octinteger: "0" ("o" | "O") octdigit ([""] octdigit)* hexinteger: "0" ("x" | "X") hexdigit ([""] hexdigit)* bininteger: "0" ("b" | "B") bindigit (["_"] bindigit)*

The idea that the second alternative "forc[es] our tastes on everyone" while the first does not is bogus. The first alternative also prohibits things which are a matter of taste:

prohibited in both alternatives

0_xDEADBEEF 0._1234 1.2e_99 -1 1j

I think that there is broad agreement that:

and only minor disagreement about:

Can we have a show of hands, in favour or against the above two? And then perhaps Guido can rule on this one way or the other and we can get back to arguing about more important matters? :-)

In case it isn't obvious, I prefer to say No to allowing underscores after the base specifier, or before the decimal point, exponent and complex suffix.

-- Steve

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