[Python-Dev] RFC: PEP 509: Add a private version to dict

[Émanuel Barry]

> From Armin Rigo
> Sent: Thursday, April 14, 2016 4:42 PM
> To: Victor Stinner
> Cc: Python Dev
> Subject: Re: [Python-Dev] RFC: PEP 509: Add a private version to dict
> 
> Hi Victor,
> 
> On 14 April 2016 at 17:19, Victor Stinner <victor.stinner at gmail.com> wrote:
> > Each time a dictionary is created, the global
> > version is incremented and the dictionary version is initialized to the
> > global version.
> 
> A detail, but why not set the version tag of new empty dictionaries to
> zero, always?   Same after a clear().  This would satisfy the
> condition: equality of the version tag is supposed to mean "the
> dictionary content is precisely the same".

>From Victor's original post:

"Globally unique identifier is a requirement for Yury's patch
optimizing method calls ( https://bugs.python.org/issue26110 ). It
allows to check for free if the dictionary was replaced."

I think it's a good design idea, and there's no chance that this counter will ever overflow (I think Victor is using 64-bit unsigned integer). I don't think there's really any drawback to using a global vs per-dict counter (but Victor is better placed to answer that :))

-Emanuel

~Ducks lay where no programmer has ever been~