Requests 2.34.0 changed the stream detection in PreparedRequest.prepare_body() from hasattr(data, "__iter__") to isinstance(data, Iterable). This breaks file-like wrappers that expose __iter__/read/tell/seek via __getattr__ delegation (e.g. tqdm.wrapattr), because isinstance(..., Iterable) only checks the class MRO, not dynamic attribute delegation. As a result, _body_position is never recorded and the body cannot be rewound on 307/308 redirects.

Expected Result

Upload completes successfully through the redirect, as it did in 2.33.1.

Actual Result

The redirected request sends an empty/consumed body. The server receives no data and the request times out:

requests.exceptions.ReadTimeout: HTTPSConnectionPool(...): Read timed out. (read timeout=30)

Reproduction Steps

import os
import requests
from tqdm import tqdm

with open("testfile.txt", "wb") as f:
    f.write(b"hello world " * 1000)

with open("testfile.txt", "rb") as f:
    with tqdm.wrapattr(f, "read", total=os.path.getsize("testfile.txt")) as wrapped:
        # Any endpoint that 307 redirects to a presigned S3 URL
        requests.put("https://your-api.example.com/upload", data=wrapped, timeout=30)

System Information

$ python -m requests.help

{
  "chardet": {
    "version": null
  },
  "charset_normalizer": {
    "version": "3.4.7"
  },
  "cryptography": {
    "version": ""
  },
  "idna": {
    "version": "3.13"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.13.5"
  },
  "platform": {
    "release": "24.6.0",
    "system": "Darwin"
  },
  "pyOpenSSL": {
    "openssl_version": "",
    "version": null
  },
  "requests": {
    "version": "2.34.0"
  },
  "system_ssl": {
    "version": "30000120"
  },
  "urllib3": {
    "version": "2.5.0"
  },
  "using_charset_normalizer": true,
  "using_pyopenssl": false
}