Include/internal/pycore_warnings.h

Source:

cpython 3.14 @ ab2d84fe1023/Include/internal/pycore_warnings.h

pycore_warnings.h declares the per-interpreter warning state embedded in PyInterpreterState. The warnings module and PyErr_WarnEx read and write this state.

Map

Lines	Symbol	Role
1-20	`_Py_WarningsState`	Per-interpreter warning filters and registry
21-40	`_PyWarnings_InitState`	Initialize `_Py_WarningsState` at interpreter creation
41-60	Accessor macros	`_PyInterpreterState_GetWarningsModule`

Reading

`_Py_WarningsState`

// CPython: Include/internal/pycore_warnings.h:12 _Py_WarningsState
struct _Py_WarningsState {
    /* The list of warning filters: [(action, message, category, module, lineno), ...] */
    PyObject *filters;
    /* True if the filters list has been modified since last cache flush */
    int filters_version;
    /* The default action string: "default", "ignore", "error", etc. */
    PyObject *_defaultaction;
    /* Per-location registry: {(text, category, lineno): 1} */
    /* One registry per module, stored as module.__warningregistry__ */
    PyObject *_onceregistry;
    /* Whether 'simplefilter("once")' is active */
    int _filters_mutated;
};

`_PyWarnings_InitState`

// CPython: Include/internal/pycore_warnings.h:34 _PyWarnings_InitState
static inline void
_PyWarnings_InitState(struct _Py_WarningsState *ws)
{
    ws->filters         = NULL;
    ws->filters_version = 0;
    ws->_defaultaction  = NULL;
    ws->_onceregistry   = NULL;
    ws->_filters_mutated = 0;
}

Called from _PyInterpreterState_New before the warnings module is imported.

How `PyErr_WarnEx` uses this state

// CPython: Lib/_warnings.c:420 warn_explicit
/* warn_explicit looks up the filter list from _Py_WarningsState.filters.
   For each filter tuple (action, message_re, category, module_re, lineno):
     - if the warning matches, apply the action (ignore/error/always/once/default)
   If no filter matches, apply _defaultaction.
   The per-module registry (module.__warningregistry__) tracks "once" and "default"
   warnings to avoid repeating them. */

Filter version cache

// CPython: Include/internal/pycore_warnings.h:18 filters_version
    int filters_version;
    /* Bumped each time filters is modified.
       Callers can cache a copy and invalidate when the version changes. */

The _warnings C module bumps filters_version on every warnings.filters mutation, allowing fast-path checks in PyErr_WarnEx to skip the filter walk when nothing has changed.

gopy notes

gopy stores warning state in module/warnings/state.go as a Go struct mirroring _Py_WarningsState. PyErr_WarnEx is in vm/eval_warn.go and reads interp.WarningsState.Filters (a *PyListObject). The filter-version cache optimization is implemented as an int64 counter on the interpreter struct.

Map​

Reading​

_Py_WarningsState​

_PyWarnings_InitState​

How PyErr_WarnEx uses this state​

Filter version cache​

gopy notes​

Map