Fix prepare_body stream detection for __getattr__-based file wrappers

[k223kim]

Resolves #7432 .

Add hasattr(data, "__iter__") as a fallback stream detector:

if (
    isinstance(data, Iterable) or hasattr(data, "__iter__")
) and not isinstance(data, (str, bytes, list, tuple, Mapping)):

This catches file-like objects that proxy their interface through __getattr__, restoring the 2.33.1 behavior without reverting the isinstance(Iterable) modernization for standard iterables.

[nateprewitt]

Hi @k223kim,

This PR has quite a few oddities in it, did you happen to use an LLM to generate it? There are unrelated tests and the change itself is wrong (at least for the issue you reported).

[k223kim]

Hey @nateprewitt , thanks for the review!
I did use llm to get help with mimicking the tqdm behavior on the test - but not for the fix itself 😄 The test ensures that correct objects are detected as a stream. + I believe this did fix the issue that I was having with tqdm wrapper + redirect with the latest version of requests. Would you explain how this fix is wrong? Happy to adjust as needed.

[k223kim]

Perhaps - I can be more precise with the if-statement and just restoring it to hasattr(data, "__iter__").
i.e.

if (
    isinstance(data, Iterable) or hasattr(data, "__iter__")
) and not isinstance(data, (str, bytes, list, tuple, Mapping)):

If this sounds better, happy to adjust test accordingly.

[nateprewitt]

Yep, it should be __iter__ instead of read, otherwise we're adding new semantics to the check that didn't exist in 2.33.1 either.

The tests are engraining a lot of tqdm/use case specific semantics into the test suite that I'm not sure we want. While this may work, I don't really want to call it a "supported pattern" because that tends to lead to other areas that didn't support this before getting PRs to "fix" support.

I think it's unlikely this changes again in the future, the __iter__ check was there for ~12 years, but if we want to be really safe, a single test like this is probably sufficient:

 def test_getattr_proxy_stream_follows_redirect(self, httpbin):
     """Ensure stream wrappers that don't implement __iter__ directly are still detected."""
 
     class AttrProxy:
         def __init__(self):
             self._file = io.BytesIO(b"data")
 
         def __getattr__(self, name):
             return getattr(self._file, name)
 
     r = requests.post(httpbin("redirect-to?url=/post&status_code=307"), data=AttrProxy())
     assert r.json()["data"] == "data"

[k223kim]

@nateprewitt Makes sense. Adjusted the PR 😄 Would appreciate it if you can take a look!

[nateprewitt]

One minor tweak for readability, but otherwise this looks good. Thanks @k223kim!