cpython/Tools/c-analyzer
Petr Viktorin 7dfa048bbb
gh-135228: Create __dict__ and __weakref__ descriptors for object (GH-136966)
This partially reverts #137047, keeping the tests for GC collectability of the
original class that dataclass adds `__slots__` to.
The reference leaks solved there are instead solved by having the `__dict__` &
`__weakref__` descriptors not tied to (and referencing) their class.

Instead, they're shared between all classes that need them (within
an interpreter).
The `__objclass__` ol the descriptors is set to `object`, since these
descriptors work with *any* object. (The appropriate checks were already
made in the get/set code, so the `__objclass__` check was redundant.)

The repr of these descriptors (and any others whose `__objclass__` is `object`)
now doesn't mention the objclass.

This change required adjustment of introspection code that checks
`__objclass__` to determine an object's “own” (i.e. not inherited) `__dict__`.
Third-party code that does similar introspection of the internals will also
need adjusting.


Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
2025-08-18 14:25:51 +02:00
..
c_analyzer clearer error and suggestion when c-analyzer cannot read ignored.tsv (#129423) 2025-01-30 11:38:52 +00:00
c_common
c_parser gh-122943: Rework support of var-positional parameter in Argument Clinic (GH-122945) 2024-11-07 23:40:03 +02:00
cpython gh-135228: Create __dict__ and __weakref__ descriptors for object (GH-136966) 2025-08-18 14:25:51 +02:00
distutils
c-analyzer.py
check-c-globals.py
must-resolve.sh
README
table-file.py
TODO gh-132661: Implement PEP 750 (#132662) 2025-04-30 11:46:41 +02:00

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# C Globals and CPython Runtime State.

CPython's C code makes extensive use of global variables.  Each global
falls into one of several categories:

* (effectively) constants (incl. static types)
* globals used exclusively in main or in the REPL
* freelists, caches, and counters
* process-global state
* module state
* Python runtime state

Of the different categories, the last two are problematic and
generally should not exist in the codebase.

Globals that hold module state (i.e. in Modules/*.c) cause problems
when multiple interpreters are in use.  For more info, see PEP 3121,
which addresses the situation for extension modules in general.

Globals in the last category should be avoided as well.  The problem
isn't with the Python runtime having state.  Rather, the problem is with
that state being spread throughout the codebase in dozens of individual
globals.  Unlike the other globals, the runtime state represents a set
of values that are constantly shifting in a complex way.  When they are
spread out it's harder to get a clear picture of what the runtime
involves.  Furthermore, when they are spread out it complicates efforts
that change the runtime.

Consequently, the globals for Python's runtime state have been
consolidated under a single top-level _PyRuntime global. No new globals
should be added for runtime state.  Instead, they should be added to
_PyRuntimeState or one of its sub-structs.  The check-c-globals script
should be run to ensure that no new globals have been added:

  python3 Tools/c-analyzer/check-c-globals.py

You can also use the more generic tool:

  python3 Tools/c-analyzer/c-analyzer.py

If it reports any globals then they should be resolved.  If the globals
are runtime state then they should be folded into _PyRuntimeState.