René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"functools.singledispatch registration prioritizes the types of normal arguments before positional-only ones","articleBody":"# Bug report\n\n### Bug description:\n\nDecorator-based `functools.singledispatch` registration prioritizes the types of normal arguments before positional-only ones when getting [\"the type of the first argument\"](https://docs.python.org/3/library/functools.html#functools.singledispatch).\n\nThis means that a function of `def f(pos: str, /, other: int)` will be registered to be dispatched for `other`'s type (`int`) instead of `pos` (`str`).\n\nTo reproduce:\n\n```python\nimport functools\n\n@functools.singledispatch\ndef f(arg, /, extra):\n    return f\"{arg}: undispatched type\"\n\n@f.register\ndef f_int(arg: int, /, extra: str):\n    return f\"{arg} is a {type(arg)} (dispatched by int)\"\n\n@f.register\ndef f_str(arg: str, /, extra: int):\n    return f\"{arg} is a {type(arg)} (dispatched by str)\"\n\nprint(f(None, \"extra\"))\nprint(f(1, \"extra\"))\nprint(f(\"s\", \"extra\"))\n```\n\nResult:\n```\nNone: undispatched type\n1 is a \u003cclass 'int'\u003e (dispatched by str)\ns is a \u003cclass 'str'\u003e (dispatched by int)\n```\n\nExpected:\n```\nNone: undispatched type\n1 is a \u003cclass 'int'\u003e (dispatched by int)\ns is a \u003cclass 'str'\u003e (dispatched by str)\n```\n\n\n### CPython versions tested on:\n\n3.9, 3.10, 3.11, 3.12, 3.13, 3.14, CPython main branch\n\n### Operating systems tested on:\n\nmacOS\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-143888\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/pR0Ps","@type":"Person","name":"pR0Ps"},"datePublished":"2026-01-15T18:53:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/143886/cpython/issues/143886"}