> this is because _Py_DisplaySourceLine() (in Python/traceback.c) assumes that io.TextIOWrapper() returned a stream object, and tries to call its close()  method. in case calling close() fails, _Py_DisplaySourceLine() just calls PyErr_Clear().

I consider that _Py_DisplaySourceLine() is right to expect that io.TextIOWrapper() creates a stream object. If the TextIOWrapper creation fails, it calls binary.close() to prevent a resource warning. Here your function doesn't fail but returns None which is really not expected.


> def _bad_TextIOWrapper(*args): return None
> io.TextIOWrapper = _bad_TextIOWrapper

I don't see why Python should support such strange TextIOWrapper type. I simply suggest to close the issue as WONTFIX.