_Py_DecodeUTF8Ex() creates surrogate pairs with 16-bit wchar_t (on Windows), whereas input bytes should be escaped. I'm quite sure that it's a bug.

Extract of _Py_DecodeUTF8Ex() code, there is an explicit "write a surrogate pair" comment:

#if SIZEOF_WCHAR_T == 4
        ch = ucs4lib_utf8_decode(&s, e, (Py_UCS4 *)unicode, &outpos);
#else
        ch = ucs2lib_utf8_decode(&s, e, (Py_UCS2 *)unicode, &outpos);
#endif
        if (ch > 0xFF) {
#if SIZEOF_WCHAR_T == 4
            Py_UNREACHABLE();
#else
            assert(ch > 0xFFFF && ch <= MAX_UNICODE);
            /* write a surrogate pair */
            unicode[outpos++] = (wchar_t)Py_UNICODE_HIGH_SURROGATE(ch);
            unicode[outpos++] = (wchar_t)Py_UNICODE_LOW_SURROGATE(ch);
#endif
        }

Could you show an example please?

> Could you show an example please?

I saw an issue when reading the code, I didn't try to trigger the issue using real code yet.

I don't see anything wrong.

> I don't see anything wrong.

I write a C function to test _Py_DecodeUTF8Ex():

* surrogateescape=0 fails with a decoding error as expected
* surrogateescape=1 escapes the bytes as expected as: '\udced\udcb2\udc80'

Ok, I just misunderstood the code: the decoder is fine!