[issue42317] Docs of `typing.get_args`: Mention that due to caching of typing generics the order of arguments for Unions can be different from the one of the returned tuple

[Guido van Rossum]

Guido van Rossum <guido at python.org> added the comment:

Agreed it's mildly sad, and I wish the cache could preserve the order in List[Union[int, str]], but for that to work we'd have to change how the cache works, which feels complex, or we'd have to chance things so that Union[int, str] != Union[str, int], which seems wrong as well (and we've had them equal for many releases so this would break code).

Fixing the cache would require adding a new comparison method to all generic type objects, and that just doesn't seem worth the effort (but I'd be open to this solution in the future).

So for now, let's document that get_args() may swap Union arguments.

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stage:  -> needs patch

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<https://bugs.python.org/issue42317>
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