3.9
bpo-39674: Revert "bpo-37330: open() no longer accept 'U' in file mode (GH-16959)" (GH-18767)
bpo-40268: Remove unused structmember.h includes (GH-19530)
bpo-11410: Standardize and use symbol visibility attributes across POSIX and Windows. (GH-16347)
bpo-44687: Ensure BufferedReader objects with unread buffers can peek even when the underlying file is closed (GH-28457)
bpo-43499: Silence compiler warnings about using legacy C API on Windows (GH-24873)
bpo-25415: Remove confusing sentence from IOBase docstrings (PR-31631)