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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"long_subtype_new underallocates for zero","articleBody":"When creating `int` instances, we [always allocate](https://github.com/python/cpython/blob/ef633e5000222a3dba74473c49d6a81fca0a44ec/Objects/longobject.c#L157) space for and initialise at least one digit, since the `medium_value` function that's used for fast paths [assumes the existence](https://github.com/python/cpython/blob/ef633e5000222a3dba74473c49d6a81fca0a44ec/Objects/longobject.c#L33) of that digit. This change was introduced for Python 3.11 in PR #27832.\r\n\r\nHowever, the corresponding change in `long_subtype_new` was missed; this results in us asking for zero digits in the case of creating an instance of a subclass of `int` with value zero - e.g.,\r\n\r\n```python\r\nclass MyInt(int):\r\n    pass\r\n\r\nmyint = MyInt()  # problem\r\n```\r\n\r\nThat's then a problem if `myint` is used in a context where `medium_value` might be called on it, for example as in `int(myint)`.\r\n\r\nWe've got away with this so far because of a compensating _overallocation_ issue: see #81381; this bug blocked an attempt to address #81381 in #100855. But I believe this should still be fixed.\r\n\r\nI'll make a PR shortly.\r\n\r\n\r\n\u003c!-- gh-linked-prs --\u003e\r\n### Linked PRs\r\n* gh-101038\r\n* gh-101219\n\u003c!-- /gh-linked-prs --\u003e\r\n","author":{"url":"https://github.com/mdickinson","@type":"Person","name":"mdickinson"},"datePublished":"2023-01-14T16:47:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/101037/cpython/issues/101037"}