the following code causes a ResourceWarning:

import io
def _bad_TextIOWrapper(*args):
    return None
io.TextIOWrapper = _bad_TextIOWrapper
1/0


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().


maybe _Py_DisplaySourceLine() should try to call binary.close() in such cases?

I also thought about adding a check such as:
PyObject_IsInstance(fob, (PyObject*)&PyTextIOWrapper_Type);
but I am not sure whether we should use PyTextIOWrapper_Type outside of the io
module.

> 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.

I think it should be closed as "not a bug".

If io.TextIOWrapper() is successful, it is responsible for property closing a binary file. The bug is in user code, not in the interpreter code.

_Py_DisplaySourceLine() correctly calls binary.close() if io.TextIOWrapper() failed.

Ok, thanks for the confirmation Serhiy. I close the bug.