The "XMLParser.__init__()" method in "_elementtree.c" contains this code:

    self->handle_start = PyObject_GetAttrString(target, "start");
    self->handle_data = PyObject_GetAttrString(target, "data");
    self->handle_end = PyObject_GetAttrString(target, "end");
    self->handle_comment = PyObject_GetAttrString(target, "comment");
    self->handle_pi = PyObject_GetAttrString(target, "pi");
    self->handle_close = PyObject_GetAttrString(target, "close");
    self->handle_doctype = PyObject_GetAttrString(target, "doctype");
    PyErr_Clear();

This ignores all exceptions, not only AttributeError.
It also passes live exceptions into the later lookup calls, which may execute arbitrary user code.