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Add Py_GetConstant() and Py_GetConstantBorrowed() (#87)
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‎docs/api.rst

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@@ -192,6 +192,15 @@ Python 3.12
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Not available on PyPy.
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.. c:function:: PyObject* Py_GetConstant(unsigned int constant_id)
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See `Py_GetConstant() documentation <https://docs.python.org/dev/c-api/object.html#c.Py_GetConstant>`__.
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.. c:function:: PyObject* Py_GetConstantBorrowed(unsigned int constant_id)
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See `Py_GetConstantBorrowed() documentation <https://docs.python.org/dev/c-api/object.html#c.Py_GetConstantBorrowed>`__.
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Not supported:
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* ``PyDict_AddWatcher()``, ``PyDict_Watch()``.

‎docs/changelog.rst

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@@ -1,6 +1,11 @@
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Changelog
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=========
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* 2024-03-21: Add functions:
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* ``Py_GetConstant()``
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* ``Py_GetConstantBorrowed()``
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* 2024-03-09: Add hash constants:
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* ``PyHASH_BITS``

‎pythoncapi_compat.h

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Original file line numberDiff line numberDiff line change
@@ -1209,6 +1209,83 @@ static inline int PyTime_PerfCounter(PyTime_t *result)
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#endif
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// gh-111545 added Py_GetConstant() and Py_GetConstantBorrowed()
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// to Python 3.13.0a6
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#if PY_VERSION_HEX < 0x030D00A6
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#define Py_CONSTANT_NONE 0
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#define Py_CONSTANT_FALSE 1
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#define Py_CONSTANT_TRUE 2
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#define Py_CONSTANT_ELLIPSIS 3
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#define Py_CONSTANT_NOT_IMPLEMENTED 4
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#define Py_CONSTANT_ZERO 5
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#define Py_CONSTANT_ONE 6
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#define Py_CONSTANT_EMPTY_STR 7
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#define Py_CONSTANT_EMPTY_BYTES 8
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#define Py_CONSTANT_EMPTY_TUPLE 9
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static inline PyObject* Py_GetConstant(unsigned int constant_id)
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{
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static PyObject* constants[Py_CONSTANT_EMPTY_TUPLE + 1] = {NULL};
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if (constants[Py_CONSTANT_NONE] == NULL) {
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constants[Py_CONSTANT_NONE] = Py_None;
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constants[Py_CONSTANT_FALSE] = Py_False;
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constants[Py_CONSTANT_TRUE] = Py_True;
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constants[Py_CONSTANT_ELLIPSIS] = Py_Ellipsis;
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constants[Py_CONSTANT_NOT_IMPLEMENTED] = Py_NotImplemented;
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constants[Py_CONSTANT_ZERO] = PyLong_FromLong(0);
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if (constants[Py_CONSTANT_ZERO] == NULL) {
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goto fatal_error;
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}
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constants[Py_CONSTANT_ONE] = PyLong_FromLong(1);
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if (constants[Py_CONSTANT_ONE] == NULL) {
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goto fatal_error;
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}
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constants[Py_CONSTANT_EMPTY_STR] = PyUnicode_FromStringAndSize("", 0);
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if (constants[Py_CONSTANT_EMPTY_STR] == NULL) {
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goto fatal_error;
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}
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constants[Py_CONSTANT_EMPTY_BYTES] = PyBytes_FromStringAndSize("", 0);
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if (constants[Py_CONSTANT_EMPTY_BYTES] == NULL) {
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goto fatal_error;
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}
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constants[Py_CONSTANT_EMPTY_TUPLE] = PyTuple_New(0);
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if (constants[Py_CONSTANT_EMPTY_TUPLE] == NULL) {
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goto fatal_error;
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}
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// goto dance to avoid compiler warnings about Py_FatalError()
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goto init_done;
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fatal_error:
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// This case should never happen
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Py_FatalError("Py_GetConstant() failed to get constants");
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}
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init_done:
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if (constant_id <= Py_CONSTANT_EMPTY_TUPLE) {
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return Py_NewRef(constants[constant_id]);
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}
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else {
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PyErr_BadInternalCall();
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return NULL;
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}
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}
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static inline PyObject* Py_GetConstantBorrowed(unsigned int constant_id)
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{
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PyObject *obj = Py_GetConstant(constant_id);
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Py_XDECREF(obj);
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return obj;
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}
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#endif
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#ifdef __cplusplus
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}
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#endif

‎tests/test_pythoncapi_compat_cext.c

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@@ -1573,6 +1573,91 @@ test_time(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
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#endif
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15751575

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static void
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check_get_constant(PyObject* (*get_constant)(unsigned int), int borrowed)
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{
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#define CLEAR(var) if (!borrowed) { Py_DECREF(var); }
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PyObject *obj, *expected;
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// Py_CONSTANT_NONE
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obj = get_constant(Py_CONSTANT_NONE);
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assert(obj == Py_None);
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CLEAR(obj);
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// Py_CONSTANT_FALSE
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obj = get_constant(Py_CONSTANT_FALSE);
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assert(obj = Py_False);
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CLEAR(obj);
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// Py_CONSTANT_TRUE
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obj = get_constant(Py_CONSTANT_TRUE);
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assert(obj == Py_True);
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CLEAR(obj);
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// Py_CONSTANT_ELLIPSIS
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obj = get_constant(Py_CONSTANT_ELLIPSIS);
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assert(obj == Py_Ellipsis);
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CLEAR(obj);
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// Py_CONSTANT_NOT_IMPLEMENTED
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obj = get_constant(Py_CONSTANT_NOT_IMPLEMENTED);
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assert(obj == Py_NotImplemented);
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CLEAR(obj);
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// Py_CONSTANT_ZERO
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obj = get_constant(Py_CONSTANT_ZERO);
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expected = PyLong_FromLong(0);
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assert(expected != NULL);
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assert(Py_TYPE(obj) == &PyLong_Type);
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assert(PyObject_RichCompareBool(obj, expected, Py_EQ) == 1);
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CLEAR(obj);
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Py_DECREF(expected);
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// Py_CONSTANT_ONE
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obj = get_constant(Py_CONSTANT_ONE);
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expected = PyLong_FromLong(1);
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assert(expected != NULL);
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assert(Py_TYPE(obj) == &PyLong_Type);
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assert(PyObject_RichCompareBool(obj, expected, Py_EQ) == 1);
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CLEAR(obj);
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Py_DECREF(expected);
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// Py_CONSTANT_EMPTY_STR
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obj = get_constant(Py_CONSTANT_EMPTY_STR);
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assert(Py_TYPE(obj) == &PyUnicode_Type);
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#if PY_VERSION_HEX >= 0x03030000
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assert(PyUnicode_GetLength(obj) == 0);
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#else
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assert(PyUnicode_GetSize(obj) == 0);
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#endif
1634+
CLEAR(obj);
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// Py_CONSTANT_EMPTY_BYTES
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obj = get_constant(Py_CONSTANT_EMPTY_BYTES);
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assert(Py_TYPE(obj) == &PyBytes_Type);
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assert(PyBytes_Size(obj) == 0);
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CLEAR(obj);
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// Py_CONSTANT_EMPTY_TUPLE
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obj = get_constant(Py_CONSTANT_EMPTY_TUPLE);
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assert(Py_TYPE(obj) == &PyTuple_Type);
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assert(PyTuple_Size(obj) == 0);
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CLEAR(obj);
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1648+
#undef CLEAR
1649+
}
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static PyObject *
1653+
test_get_constant(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
1654+
{
1655+
check_get_constant(Py_GetConstant, 0);
1656+
check_get_constant(Py_GetConstantBorrowed, 1);
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Py_RETURN_NONE;
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}
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static struct PyMethodDef methods[] = {
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{"test_object", test_object, METH_NOARGS, _Py_NULL},
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{"test_py_is", test_py_is, METH_NOARGS, _Py_NULL},
@@ -1609,6 +1694,7 @@ static struct PyMethodDef methods[] = {
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#ifdef TEST_PYTIME
16101695
{"test_time", test_time, METH_NOARGS, _Py_NULL},
16111696
#endif
1697+
{"test_get_constant", test_get_constant, METH_NOARGS, _Py_NULL},
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{_Py_NULL, _Py_NULL, 0, _Py_NULL}
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};
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