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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"C API: Add internal C API to build a tuple: _PyTupleBuilder","articleBody":"The current Python C API PyTuple_New() to build a tuple has multiple flaws:\r\n\r\n* The Python tuple object is immediately tracked by the GC, whereas its items are initialized to NULL (inconsistent tuple)\r\n* The PyTuple_SET_ITEM() function must only used on a tuple while is being created\r\n\r\nI propose adding a new internal C API to build a tuple: _PyTupleBuilder.\r\n\r\n* User of the API doesn't access the tuple directly but uses higher API\r\n* Over-allocate the tuple (by 25%) to reduce the number of _PyTuple_Resize() calls\r\n* _PyTupleBuild_Append() grows the tuple if needed\r\n* _PyTupleBuild_AppendUnsafe() is a thin wrapper to PyTuple_SET_ITEM()\r\n* Only track the tuple once its fully initialized: correct size, all items are set\r\n* Less error-prone API\r\n\r\nLater, once we will consider this API stable, we can add it to the public C API and deprecate the old API to create an incomplete tuple:\r\n\r\n* PyTuple_New()\r\n* PyTuple_SetItem()\r\n* PyTuple_SET_ITEM()\r\n* _PyTuple_Resize()\r\n\r\nSee https://github.com/capi-workgroup/problems/issues/56 for details on problems caused by API which let creating incomplete/inconsistent objects.\r\n\r\n\u003c!-- gh-linked-prs --\u003e\r\n### Linked PRs\r\n* gh-107139\r\n* gh-107183\n\u003c!-- /gh-linked-prs --\u003e\r\n","author":{"url":"https://github.com/vstinner","@type":"Person","name":"vstinner"},"datePublished":"2023-07-23T15:37:44.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":10},"url":"https://github.com/107137/cpython/issues/107137"}