[Python-ideas] Allow mutable builtin types (optionally)

Eloi Gaudry Eloi.Gaudry at fft.be
Tue Jun 26 10:45:23 EDT 2018

the origin of this feature disappearing for built-in types:



object.__set/delattr__ allow modification of built in types, this is
known as the Carlo Verre hack:

Jython 2.3a0+ (trunk:4630:4631M, Jun 14 2008, 20:07:38)
[Java HotSpot(TM) Client VM (Apple Inc.)] on java1.5.0_13
Type "help", "copyright", "credits" or "license" for more information.
>>> object.__setattr__(str, 'lower', str.upper)
>>> 'dammit Carlo!'.lower()

but I do not see any reason why having an explicit flag for python extensions written in C to declare their types as static struct, and still be able to change their __setattr__, __getattr__, etc. slots would not make sense.

extensions and core types have not the same constraints and purposes, this should be reflected on the capabilities the first would have somewhere then.

From: Eloi Gaudry
Sent: Tuesday, June 26, 2018 4:27:18 PM
To: python-ideas at python.org
Subject: Re: [Python-ideas] Allow mutable builtin types (optionally)

some literature:



where it is stated that python C struct type should not be able to have their attributes changed.

but the extension needs is clearly not taken into account.

From: Python-ideas <python-ideas-bounces+eloi.gaudry=fft.be at python.org> on behalf of Eloi Gaudry <Eloi.Gaudry at fft.be>
Sent: Thursday, June 21, 2018 5:26:37 PM
To: python-ideas at python.org; encukou at gmail.com
Subject: Re: [Python-ideas] Allow mutable builtin types (optionally)

This request didn't have a lot of traction, but I still consider this is something that would need to be supported (2 lines of code to be changed; no regression so far with python 2 and python 3).

My main points are:

- HEAP_TYPE is not really used (as anyone being using it ?)

- HEAP_TYPE serves other purposes

- extension would benefit for allowing direct access to any of its type attributes

Petr, what do you think ?


From: Python-ideas <python-ideas-bounces+eloi.gaudry=fft.be at python.org> on behalf of Eloi Gaudry <Eloi.Gaudry at fft.be>
Sent: Tuesday, May 8, 2018 9:26:47 AM
To: encukou at gmail.com; python-ideas at python.org
Subject: Re: [Python-ideas] Allow mutable builtin types (optionally)

On Mon, 2018-05-07 at 15:23 -0400, Petr Viktorin wrote:
> On 05/07/18 11:37, Eloi Gaudry wrote:
> > I mean, to my knowledge, there is no reason why a type should be
> > allocated on the heap (https://docs.python.org/2/c-api/typeobj.html
> > ) to
> > be able to change its attributes at Python level.
> One reason is sub-interpreter support: you can have multiple
> interpreters per process, and those shouldn't influence each other.
> (see https://docs.python.org/3/c-api/init.html#sub-interpreter-suppor
> t)
> With heap types, each sub-interpreter can have its own copy of the
> type
> object. But with builtins, changes done in one interpreter would be
> visible in all the others.

Yes, this could be a reason, but if you don't rely on such a feature
neither implicitly nor explicitly ?

I mean, our types are built-in and should be considered as immutable
across interpreters. And we (as most users I guess) are only running
one interpreter.

In case several intepreters are used, it would make sense to have a
non-heap type that would be seen as a singleton across all of them, no
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