With pyerr_printex.patch we get the following correct results (rc=120 is set by Py_Main() after Py_FinalizeEx() returns with an error):

$ ./python memerr.py 5 12
set_nomemory(0, 5)
result = _PythonRunResult(rc=1, out=b'', err=b'MemoryError\n\nDuring handling of the above exception, another exception occurred:\n\nMemoryError')
=============================
set_nomemory(0, 6)
result = _PythonRunResult(rc=1, out=b'', err=b'sys.excepthook is missing\nMemoryError\n\nDuring handling of the above exception, another exception occurred:\n\nMemoryError')
=============================
set_nomemory(0, 7)
result = _PythonRunResult(rc=1, out=b'', err=b'sys.excepthook is missing\nMemoryError\n\nDuring handling of the above exception, another exception occurred:\n\nMemoryError')
=============================
set_nomemory(0, 8)
result = _PythonRunResult(rc=1, out=b'', err=b'sys.excepthook is missing\nobject  : MemoryError()\ntype    : MemoryError\nrefcount: 1\naddress : 0x7f7ae1be3eb0\nlost sys.stderr')
=============================
set_nomemory(0, 9)
result = _PythonRunResult(rc=1, out=b'', err=b'sys.excepthook is missing\nobject  : \ntype    : MemoryError\nrefcount: 1\naddress : 0x7f8aead15eb0\nlost sys.stderr')
=============================
set_nomemory(0, 10)
result = _PythonRunResult(rc=1, out=b'', err=b'sys.excepthook is missing\nobject  : \ntype    : MemoryError\nrefcount: 1\naddress : 0x7f7b489d1eb0\nlost sys.stderr')
=============================
set_nomemory(0, 11)
result = _PythonRunResult(rc=1, out=b'', err=b'sys.excepthook is missing\nobject  : \ntype    : MemoryError\nrefcount: 1\naddress : 0x7ff97365eeb0\nlost sys.stderr')
=============================
set_nomemory(0, 12)
result = _PythonRunResult(rc=120, out=b'', err=b"sys.excepthook is missing\nobject  : \ntype    : MemoryError\nrefcount: 1\naddress : 0x7f559c9e0eb0\nlost sys.stderr\nException ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' encoding='UTF-8'>\nMemoryError")
=============================