Bug report

Bug description:

So I am not entirely sure whether this is unintended behaviour, but it is definitely a noticeable change between 3.11 and 3.12 that is rather unintuitive

import pickle from io import BytesIO, TextIOWrapper class EncodedFile(TextIOWrapper): def __getstate__(self): return "string" def __setstate__(self, state): pass file = EncodedFile(BytesIO(b"string")) pickle.dumps(file)

This works in Python 3.11 and 3.10, but fails in 3.12 with

pickle.dumps(file) TypeError: cannot pickle 'EncodedFile' instances

CPython versions tested on:

3.10, 3.11, 3.12

Operating systems tested on:

macOS

Linked PRs

• gh-122559: Synchronize C and Python implementation of the io module about pickling #122628
• [3.13] gh-122559: Synchronize C and Python implementation of the io module about pickling (GH-122628) #133381