[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

[Dominik V.]

Dominik V. <dominik.vilsmeier1123 at gmail.com> added the comment:

Thinking more about it, I came to realize that it's not the Union that sits at the root of this behavior, but rather the caching performed by generic types in general. So if we consider

```
L1 = List[Union[int, str]]
L2 = List[Union[str, int]]
```

then `get_args(L1)[0] is get_args(L2)[0]` and so `get_args` has no influence on the order of arguments of the Union objects (they are already the same for L1 and L2).

So I think it would be more accurate to add the following sentence instead:

> If `X` is a generic type, the returned objects `(Y, Z, ...)` might not be identical to the ones used in the form `X[Y, Z, ...]` due to type caching.

Everything else follows from there (including flattening of nested Unions).

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