Posting del-flush.patch, which only calls flush() instead of close() from __del__(), except for the FileIO class. Quick analysis of resulting test failures:

These tests fail because they are obviously written to test that __del__ calls close():
* IOTest.test_IOBase_destructor
* IOTest.test_RawIOBase_destructor
* IOTest.test_BufferedIOBase_destructor
* IOTest.test_TextIOBase_destructor
* test_override_destructor as mentioned above

CBufferedReader/Writer/RandomTest.test_garbage_collection() fail because they do not free the reference to the wrapped raw file object. Similarly, CTextIOWrapperTest.test_garbage_collection() holds references to both levels of wrapped object.

TextIOWrapperTest.test_destructor() fails because it assumes the wrapped close() will be called. The data is still written to the wrapped file though.

MiscIOTest.test_warn_on_dealloc/_fd() fail because the warning message only refers to the FileIO object rather than the wrapper object.