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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Receiving vector calls in the Py_LIMITED_API","articleBody":"**Feature or enhancement**\r\n\r\nThe `PyType_FromSpec` family of functions provides a convenient and forward-compatible way mechanism for creating new types. It could in principle also be used to create _callables_ providing a PEP-590 vector call interface, which has significant performance benefits for binding libraries (see the [related discussion](https://discuss.python.org/t/ideas-for-forward-compatible-and-fast-extension-libraries-in-python-3-12/15993/12) here).\r\n\r\nOne can already specify a member named `__vectorcalloffset__` in `PyType_FromSpec`. This isn't fully working in the limited API, however. I encountered the following problems.\r\n\r\n1. The `Py_TPFLAGS_HAVE_VECTORCALL` flag is not part of the limited API.\r\n2. The `PyVectorcall_NARGS()` helper function is not part of the limited API.\r\n3. One would normally set `tp_call` to the compatibility dispatch routine `PyVectorcall_Call`. It is, however, also not part of the public ABI. \r\n4. Leaving `tp_call` unspecified is not an option. `PyType_Ready()` even throws an exception in `type_ready_pre_checks()` when `tp_call` is unspecified.\r\n\r\n**Pitch**\r\n\r\nI propose the following changes:\r\n\r\n1. Adding ``Py_TPFLAGS_HAVE_VECTORCALL``,  `PyVectorcall_NARGS()`, and `PyVectorcall_Call()` to the limited API.\r\n2. Redundant, but nice: Setting `tp_call` to `PyVectorcall_Call` when `PyType_Ready` encounters a type that doesn't have this field set.\r\n\r\nNote that vector calls can be _received_ and _performed_. This issue is just about the receiving end.\r\n\r\n**Previous discussion**\r\n\r\nSee the discord thread https://discuss.python.org/t/ideas-for-forward-compatible-and-fast-extension-libraries-in-python-3-12/15993/12.","author":{"url":"https://github.com/wjakob","@type":"Person","name":"wjakob"},"datePublished":"2022-05-26T22:28:45.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":15},"url":"https://github.com/93274/cpython/issues/93274"}