PyMemoryView_FromMemory is part of stable ABI but the flag constants (PyBUF_READ, etc.) are not

[asottile]

Feature or enhancement

I'd rather not write:

#ifndef PyBUF_READ
#define PyBUF_READ 0x100
#endif

and instead be able to rely on these even in stable abi mode

relevant error message:

whatever.c:1:30: error: ‘PyBUF_READ’ undeclared (first use in this function)

Linked PRs

• gh-98680: Add PyBUF_* constants to the Limited API listing #100018
• [3.11] gh-98680: Add PyBUF_* constants to the Limited API listing (GH-100018) #100020

[encukou]

whatever.c:1:30: error: ‘PyBUF_READ’ undeclared (first use in this function)

How did you get this error? The flags should be available with #define Py_LIMITED_API 0x030b0000 (3.11).

It's true that they weren't added to the manifest, though. Thanks for catching that!

[asottile]

anything older than 3.11 has:

#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03030000
PyAPI_FUNC(PyObject *) PyMemoryView_FromMemory(char *mem, Py_ssize_t size,
                                               int flags);
#endif

[encukou]

Ah! Of course. 3.11 added the whole buffer API and I somehow assumed PyMemoryView_FromMemory was part of that.

If we add the constants retroactively, code that compiles fine on newer Python versions might fail to compile on older ones, even with the same Py_LIMITED_API setting. I'd rather avoid that.
The #ifndef/#define you posted is a good workaround. (Pedantically, it is relying on non-limited API until 3.11, but earlier releases won't change any more so it's fine.)

[asottile]

yeah I totally understand -- my bad for not checking 3.11 otherwise this would have been more accurately just a documentation issue /o\

[encukou]

Don't feel bad at all -- an issue that's not fully triaged is better than no issue :)
Thanks for reaching out!