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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"The return value of function `math.isclose` can be somewhat misleading","articleBody":"# Documentation\r\n\r\nThe following example may be misleading to people who are not familiar with the function:\r\n\r\n```python\r\n\u003e\u003e\u003e math.isclose(math.sin(0), 0)\r\n... True\r\n\u003e\u003e\u003e math.isclose(math.sin(math.pi), 0)\r\n... False\r\n\u003e\u003e\u003e \r\n```\r\n\r\nTo a newbie, the above results seem ridiculous. Correspondingly, the result in `numpy` is as follows:\r\n\r\n```python\r\n\u003e\u003e\u003e numpy.isclose(math.sin(0), 0)\r\n... np.True_\r\n\u003e\u003e\u003e numpy.isclose(math.sin(math.pi), 0)\r\n... np.True_\r\n\u003e\u003e\u003e \r\n```\r\n\r\nFor reference, some values are given here:\r\n\r\n```python\r\n\u003e\u003e\u003e math.sin(0)\r\n... 0.0\r\n\u003e\u003e\u003e math.sin(math.pi)\r\n... 1.2246467991473532e-16\r\n\u003e\u003e\u003e \r\n```\r\n\r\nI think, the reason for this is that the default value of parameter `abs_tol` for function `math.isclose` is too small. Here are the definitions of the two functions mentioned above:\r\n\r\n```python\r\nmath.isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0)\r\nnumpy.isclose(a, b, rtol=1e-05, atol=1e-08, equal_nan=False)\r\n```\r\n\r\nI think we might need to state this in the docstring of function `math.isclose`, ~~or increase the value of the default parameter `abs_tol` appropriately.~~\r\n\r\nBy the way, the `numpy` version I'm using here is *v2.1*.\r\n\r\nIf there is something wrong with my previous content, please feel free to point it out, thank you!\r\n\r\n\r\n### CPython versions tested on:\r\n\r\n3.13\r\n\r\n### Operating systems tested on:\r\n\r\nWindows\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-126215\n* gh-126380\n* gh-126381\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/Xiaokang2022","@type":"Person","name":"Xiaokang2022"},"datePublished":"2024-10-30T03:31:04.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":16},"url":"https://github.com/126165/cpython/issues/126165"}