Oh, I see many other issues with C implementation of ElementTree.

1. If XMLParser.__init__ is called twice, it leaks references and the Expat parser.

Possible solution: use the Py_XSETREF() macro instead of simple assignment. The Expat parser needs special handling.

Other possible solution: drop __init__() and make all initialization in __new__(). But this is a solution only for 3.7 because can break compatibility.

2. If XMLParser.__init__ is not called or if it fails to initialize the Expat parser, self->entity and self->target are NULL. Later in xmlparser_getattro() they are increfed unconditionally.