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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Improve duck type compatibility of int with float","articleBody":"# Feature or enhancement\r\n\r\nFunction arguments and variables annotated with `float` should not allow value of type `int.`\r\n\r\n# Pitch\r\n\r\n[PEP484](https://peps.python.org/pep-0484/) suggested that `when an argument is annotated as having type float, an argument of type int is acceptable;`. This allows this kind of typing to be valid:\r\n\r\n`x: float = 2`\r\n\r\nBut `int` is not subtype of `float` and doesn't provide the same interface. Float provides methods that are not available in `int`:\r\n\r\n- `is_integer`\r\n- `fromhex`\r\n- `hex`\r\n\r\nThis violates LSP and is problematic especially with `is_integer`:\r\n\r\n```python\r\ndef method_requiring_whole_number_float(number: float):\r\n    if number.is_integer():\r\n        ...\r\n```\r\n\r\nThis method clearly states that it requires `float` and as an author of such code, I would expect that `is_integer` would be available if my typing is correct.\r\n\r\nThere are workarounds (`if int(number) == number:`) but they render the `is_integer` useless as it can never be safely used.\r\n\r\nJust adding the missing methods to `int` (or removing the extra methods from `float`) would not be valid solution as there are other problems stemming from the fact that `int` is not `float`. Eg.:\r\n\r\n```python\r\ndef split_whole_and_decimal(number: float) -\u003e tuple[str, str]:\r\n    return str(number).split('.')  # it's reasonable to expect that the output contains a dot `.` as  `float` does but `int` doesn't \r\n```\r\n\r\nI'm proposing an errata to PEP484 that will remove `when an argument is annotated as having type float, an argument of type int is acceptable;`.\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-100439\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/JakubTesarek","@type":"Person","name":"JakubTesarek"},"datePublished":"2022-12-15T14:17:07.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":12},"url":"https://github.com/100268/cpython/issues/100268"}