Remove public PyContextVar_GetChanged() API.

Use a private API instead (ctx._get_changed() is the Python-level API).

Author: nascheme

Doc/c-api/contextvars.rst

@@ -182,27 +182,3 @@ Context variable functions:
    Reset the state of the *var* context variable to that it was in before
    :c:func:`PyContextVar_Set` that returned the *token* was called.
    This function returns ``0`` on success and ``-1`` on error.
-
-.. c:function:: int PyContextVar_GetChanged(PyObject *var, PyObject *default_value, PyObject **value, int *changed)
-
-   Like :c:func:`PyContextVar_Get`, but also reports whether the variable was
-   changed in the current context scope.  This combines a value lookup with a
-   change check in a single HAMT lookup.
-
-   Returns ``-1`` if an error has occurred during lookup, and ``0`` if no
-   error occurred, whether or not a value was found.
-
-   On success, *\*value* is set following the same rules as
-   :c:func:`PyContextVar_Get`.  *\*changed* is set to ``1`` if the variable
-   was changed (via :c:func:`PyContextVar_Set`) in the current context scope
-   (i.e. within the current :meth:`~contextvars.Context.run` call) with a
-   value that is a different object than the inherited one.  Otherwise
-   *\*changed* is set to ``0``.  If the value was not found, *\*changed* is
-   always ``0``.
-
-   If the current context was never entered (no :meth:`~contextvars.Context.run`
-   is active), all existing bindings are considered "changed".
-
-   Except for ``NULL``, the function returns a new reference via *\*value*.
-
-   .. versionadded:: 3.15

Doc/data/refcounts.dat

@@ -400,12 +400,6 @@ PyContextVar_Reset:int:::
 PyContextVar_Reset:PyObject*:var:0:
 PyContextVar_Reset:PyObject*:token:-1:
 
-PyContextVar_GetChanged:int:::
-PyContextVar_GetChanged:PyObject*:var:0:
-PyContextVar_GetChanged:PyObject*:default_value:0:
-PyContextVar_GetChanged:PyObject**:value:+1:???
-PyContextVar_GetChanged:int*:changed::
-
 PyCFunction_New:PyObject*::+1:
 PyCFunction_New:PyMethodDef*:ml::
 PyCFunction_New:PyObject*:self:+1:

Doc/library/contextvars.rst

@@ -119,41 +119,6 @@ Context Variables
 
       The same *token* cannot be used twice.
 
-   .. method:: get_changed([default])
-
-      Like :meth:`ContextVar.get`, but returns a tuple ``(value, changed)``
-      where *changed* indicates whether the variable was changed in the
-      current context scope.
-
-      A variable is considered "changed" if :meth:`ContextVar.set` has been
-      called on it within the current :meth:`Context.run` call with a value
-      that is a different object than the inherited one.  Variables inherited
-      unchanged from a parent context scope are not considered "changed".
-      If no :meth:`Context.run` is active, all existing bindings are
-      considered "changed".  When the value comes from a default, *changed*
-      is always ``False``.
-
-      This is useful when a context variable holds a mutable object that
-      needs to be copied on first access in a new context scope to ensure
-      modifications are local to that scope::
-
-         _ctx_var = ContextVar('ctx_var')
-
-         def get_ctx():
-             try:
-                 ctx, changed = _ctx_var.get_changed()
-             except LookupError:
-                 ctx = default_context()
-                 _ctx_var.set(ctx)
-                 return ctx
-
-             if not changed:
-                 ctx = ctx.copy()
-                 _ctx_var.set(ctx)
-             return ctx
-
-      .. versionadded:: 3.15
-
 
 .. class:: Token
 

Include/cpython/context.h

@@ -100,26 +100,6 @@ PyAPI_FUNC(PyObject *) PyContextVar_Set(PyObject *var, PyObject *value);
 PyAPI_FUNC(int) PyContextVar_Reset(PyObject *var, PyObject *token);
 
 
-/* Get a value for the variable and check if it was changed.
-
-   Like PyContextVar_Get, but also reports whether the variable was
-   changed in the current context scope via a single HAMT lookup.
-
-   Returns -1 if an error occurred during lookup.
-
-   Returns 0 if no error occurred.  In this case:
-
-   - *value will be set the same as for PyContextVar_Get.
-   - *changed will be set to 1 if the variable was changed in the
-     current context scope, 0 otherwise.  If the variable was not
-     found, *changed is always 0.
-
-   '*value' will be a new ref, if not NULL.
-*/
-PyAPI_FUNC(int) PyContextVar_GetChanged(
-    PyObject *var, PyObject *default_value, PyObject **value, int *changed);
-
-
 #ifdef __cplusplus
 }
 #endif

Include/internal/pycore_context.h

@@ -59,5 +59,24 @@ PyAPI_FUNC(PyObject*) _PyContext_NewHamtForTests(void);
 PyAPI_FUNC(int) _PyContext_Enter(PyThreadState *ts, PyObject *octx);
 PyAPI_FUNC(int) _PyContext_Exit(PyThreadState *ts, PyObject *octx);
 
+/* Get a value for the variable and check if it was changed.
+
+   Like PyContextVar_Get, but also reports whether the variable was
+   changed in the current context scope via a single HAMT lookup.
+
+   Returns -1 if an error occurred during lookup.
+
+   Returns 0 if no error occurred.  In this case:
+
+   - *value will be set the same as for PyContextVar_Get.
+   - *changed will be set to 1 if the variable was changed in the
+     current context scope, 0 otherwise.  If the variable was not
+     found, *changed is always 0.
+
+   '*value' will be a new ref, if not NULL.
+*/
+PyAPI_FUNC(int) _PyContextVar_GetChanged(
+    PyObject *var, PyObject *default_value, PyObject **value, int *changed);
+
 
 #endif /* !Py_INTERNAL_CONTEXT_H */

Lib/_pydecimal.py

@@ -361,7 +361,7 @@ def getcontext():
     New contexts are copies of DefaultContext.
     """
     try:
-        context, changed = _current_context_var.get_changed()
+        context, changed = _current_context_var._get_changed()
     except LookupError:
         context = Context()
         _current_context_var.set(context)