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bpo-38787: Add PyCFunction_CheckExact() macro for exact type checks #20024

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Merged
miss-islington merged 3 commits into from
May 12, 2020
Conversation 9 Commits 3 Checks 0 Files changed
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bpo-38787: Add PyCFunction_CheckExact() macro for exact type checks #20024

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bpo-38787: Add PyCFunction_CheckExact() macro for exact type checks n…
scoder May 10, 2020
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Add news entry.
scoder May 10, 2020
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Apply suggestions from code review: move News entry, move PyCMethod_C…
scoder May 12, 2020
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3 changes: 3 additions & 0 deletions Include/cpython/methodobject.h
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Expand Up @@ -4,6 +4,9 @@

PyAPI_DATA(PyTypeObject) PyCMethod_Type;

#define PyCMethod_CheckExact(op) Py_IS_TYPE(op, &PyCMethod_Type)
#define PyCMethod_Check(op) PyObject_TypeCheck(op, &PyCMethod_Type)

/* Macros for direct access to these values. Type checks are *not*
done, so use with care. */
#define PyCFunction_GET_FUNCTION(func) \
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3 changes: 2 additions & 1 deletion Include/methodobject.h
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Expand Up @@ -13,7 +13,8 @@ extern "C" {

PyAPI_DATA(PyTypeObject) PyCFunction_Type;

#define PyCFunction_Check(op) (Py_IS_TYPE(op, &PyCFunction_Type) || (PyType_IsSubtype(Py_TYPE(op), &PyCFunction_Type)))
#define PyCFunction_CheckExact(op) Py_IS_TYPE(op, &PyCFunction_Type)

vstinner May 11, 2020

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality Hide comment

I would prefer to exclude PyCFunction_CheckExact() from the limited C API.

scoder May 12, 2020

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality Hide comment

I'm not so sure. We are changing the semantics of PyCFunction_Check() by adding a subtype that it covers. The macro is a part of the limited C-API and thus, the semantic change is a problem all by itself. Either we accept that, then we should add the "obvious" related CheckExact macro, also to the limited API. Or, we reject that change all together. I don't think the latter is an option, though.

Personally, I'd say, since it's a macro, it doesn't hurt, since it has no impact at all on the ABI. Everyone can safely copy and use that macro also on their side, so why not just add it?

vstinner May 12, 2020

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality Hide comment

I will not hold this PR just for that. We can should PyCFunction_CheckExact() as it is in Python 3.9, and revisit the issue later. I created https://bugs.python.org/issue40601 to explain my concern: I plan to work on that in Python 3.10, it's too late for Python 3.9.

encukou May 12, 2020

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Do note that PyCMethod is a bit of a hack in that PyCFunction is still not an "acceptable base type". You can't subclasstype(print), but static types happen to bypass the Py_TPFLAGS_BASETYPE check. This is one more thing to be resolved if we want all types can become heap types.
#define PyCFunction_Check(op) PyObject_TypeCheck(op, &PyCFunction_Type)

typedef PyObject *(*PyCFunction)(PyObject *, PyObject *);
typedef PyObject *(*_PyCFunctionFast) (PyObject *, PyObject *const *, Py_ssize_t);
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/C API/2020-05-10-16-39-08.bpo-38787.XzQ59O.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Add PyCFunction_CheckExact() macro for exact type checks now that we allow subtypes of PyCFunction,
as well as PyCMethod_CheckExact() and PyCMethod_Check() for the new PyCMethod subtype.
2 changes: 1 addition & 1 deletion Objects/abstract.c
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Expand Up @@ -900,7 +900,7 @@ binary_op(PyObject *v, PyObject *w, const int op_slot, const char *op_name)
Py_DECREF(result);

if (op_slot == NB_SLOT(nb_rshift) &&
PyCFunction_Check(v) &&
PyCFunction_CheckExact(v) &&
strcmp(((PyCFunctionObject *)v)->m_ml->ml_name, "print") == 0)
{
PyErr_Format(PyExc_TypeError,
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4 changes: 2 additions & 2 deletions Python/ceval.c
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Expand Up @@ -5054,7 +5054,7 @@ trace_call_function(PyThreadState *tstate,
PyObject *kwnames)
{
PyObject *x;
if (PyCFunction_Check(func)) {
if (PyCFunction_CheckExact(func) || PyCMethod_CheckExact(func)) {
C_TRACE(x, PyObject_Vectorcall(func, args, nargs, kwnames));
return x;
}
Expand Down Expand Up @@ -5115,7 +5115,7 @@ do_call_core(PyThreadState *tstate, PyObject *func, PyObject *callargs, PyObject
{
PyObject *result;

if (PyCFunction_Check(func)) {
if (PyCFunction_CheckExact(func) || PyCMethod_CheckExact(func)) {
C_TRACE(result, PyObject_Call(func, callargs, kwdict));
return result;
}
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