Hi, I am using Python2. For the following snippet, http://ideone.com/i36pKO I'd suppose the dummy_func would be invoked, but seems not. Indeed, heapq.heapify does invoke cmp_lt per here: https://hg.python.org/cpython/file/2.7/Lib/heapq.py#l136 So why this way of monkey patching failed? Regards.