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

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miss-islington merged 3 commits into from
May 12, 2020
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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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Apply suggestions from code review: move News entry, move PyCMethod_C…
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Apply suggestions from code review: move News entry, move PyCMethod_C… 
…heck*() macros out of the limited API.
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scoder committed May 12, 2020
commit 8795b9f45b41f5bfffc2855155d0a0e919c6f86c
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: 0 additions & 3 deletions Include/methodobject.h
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Expand Up @@ -16,9 +16,6 @@ PyAPI_DATA(PyTypeObject) PyCFunction_Type;
#define PyCFunction_CheckExact(op) Py_IS_TYPE(op, &PyCFunction_Type)
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@vstinner vstinner May 11, 2020

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

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@scoder scoder May 12, 2020

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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?

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@vstinner vstinner May 12, 2020

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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.

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@encukou 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)

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

typedef PyObject *(*PyCFunction)(PyObject *, PyObject *);
typedef PyObject *(*_PyCFunctionFast) (PyObject *, PyObject *const *, Py_ssize_t);
typedef PyObject *(*PyCFunctionWithKeywords)(PyObject *, PyObject *,
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0 .../2020-05-10-16-39-08.bpo-38787.XzQ59O.rst → .../2020-05-10-16-39-08.bpo-38787.XzQ59O.rst
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