[Python-Dev] Idea: Dictionary references

[Maciej Fijalkowski]

You can very easily implement this with version tags on the globals
dictionaries - means that the dictionaries have versions and the guard
checking if everything is ok just checks the version tag on globals.

Generally speaking, such optimizations have been done in the past
(even in places like pypy, but also in literature) and as soon as we
have dynamic compilation (and FAT is a form of it), you can do such
tricks.

On Thu, Dec 17, 2015 at 3:48 PM, Steven D'Aprano <steve at pearwood.info> wrote:
> On Thu, Dec 17, 2015 at 12:53:13PM +0100, Victor Stinner quoted:
>> 2015-12-17 11:54 GMT+01:00 Franklin? Lee <leewangzhong+python at gmail.com>:
>
>> > Each function keeps an indirect, automagically updated
>> > reference to the current value of the names they use,
>
> Isn't that a description of globals()? If you want to look up a name
> "spam", you grab an indirect reference to it:
>
> globals()["spam"]
>
> which returns the current value of the name "spam".
>
>
>> > and will never need to look things up again.[*]
>
> How will this work?
>
> Naively, it sounds to me like Franklin is suggesting that on every
> global assignment, the interpreter will have to touch every single
> function in the module to update that name. Something like this:
>
> # on a global assignment
> spam = 23
>
> # the interpreter must do something like this:
> for function in module.list_of_functions:
>     if "spam" in function.__code__.__global_names__:
>         function.__code__.__global_names__["spam"] = spam
>
> As I said, that's a very naive way to implement this. Unless you have
> something much cleverer, I think this will be horribly slow.
>
> And besides, you *still* need to deal with the case that the name isn't
> a global at all, but in the built-ins namespace.
>
>
> --
> Steve
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