Hello, A little mail to signal a possible memory leak in an example of the doc, not very probable, but it may happen sometimes (and more often if we're already low on memory): https://docs.python.org/2/extending/newtypes.html in: self->first = PyString_FromString(""); if (self->first == NULL) { Py_DECREF(self); return NULL; } self->last = PyString_FromString(""); if (self->last == NULL) { Py_DECREF(self); return NULL; } I think it should be (add line in bold): self->first = PyString_FromString(""); if (self->first == NULL) { Py_DECREF(self); return NULL; } self->last = PyString_FromString(""); if (self->last == NULL) { *Py_DECREF(self->first); /* self->first is != NULL if we get here. */* Py_DECREF(self); return NULL; } Best Regards, Joel Stienlet