Description

hvenev

opened on Apr 25, 2022

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Feature or enhancement

There are lots of places where a new reference to a singleton is needed. This is done in a variety of ways:

1.  obj = Py_NewRef(Py_None);

2.  obj = Py_None;
    Py_INCREF(obj);

3.  Py_INCREF(Py_None);
    obj = Py_None;

4.  obj = Py_None;
    Py_INCREF(Py_None);

5.  obj = (Py_INCREF(Py_None), Py_None);

The proposal is to add another way that can hopefully become idiomatic:

6.  obj = Py_RefNone();

The following singletons are considered:

• None
• NotImplemented
• Ellipsis
• False
• True

In the internal API, helpers for the following singletons can be added:

• The strings returned by _Py_ID and _Py_STR
• The integers 0 and 1

Pitch

One advantage of using the new helpers is that it abstracts away the necessity to increment the reference count if immortal instances are implemented.

Alternatively, if immortal instances aren't implemented and all singletons are made per-interpreter, it will slightly reduce the performance overhead by making sure that the singletons are only looked up once (compared to patterns 3, 4, and 5, where the singletons are obtained twice).

Previous discussion

Activity

1. hvenev

   added

   type-featureA feature request or enhancementA feature request or enhancement

   on Apr 25, 2022
2. erlend-aasland

   added

   topic-C-API

   on May 16, 2022
3. vstinner commented on Nov 15, 2022

   

   vstinner

   on Nov 15, 2022

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   The problem of adding Py_RefNone() is that it grows up the Python C API by 1 more function which should be:

   • tested
   • documented
   • new comers have to learn about it

   If we consider 5 singletons, we're talking about adding 5 functions. The problem is that the Python C API is already very big and is painful to maintain: see statistics on the C API.

   IMO Py_NewRef(Py_None) is short and it doesn't require to learn a new API but combine two well defined API:

   • Py_None: borrowed reference to the None singleton
   • Py_NewRef(): create a new strong reference

   See issue #99300 which replaces Py_INCREF() with Py_NewRef(). You can see there that Py_NewRef() is applicable to many cases.

   @erlend-aasland: I propose closing this issue in favor of using Py_NewRef(Py_None).

   For example, the Py_RETURN_NONE is now simply defined as return Py_NewRef(Py_None).

   Reacted by Erlend E. Aasland
4. erlend-aasland

   closed this as not plannedon Nov 15, 2022
5. vstinner commented on Nov 15, 2022

   

   vstinner

   on Nov 15, 2022

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   By the way, my experimental PR #18301 added Py_GetNone() and Py_GetNoneRef() (2 functions just for None!), but the trend is more towards immortal objects: PEP 683.

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