i was just reading old classes vs new style classes (http://www.python.org/download/releases/2.2.3/descrintro/)
and saw that Guido was saying the key in list implementation of defaultdict would be slower.
sure it made sense. but just wanted to see how much differnce it would make. i hadn’t used cProfile anywher yet.. so got it done and here it goes no surprise. the in keys implementation is slower for medium -big dictionaries… Here are the results on github(https://github.com/anandjeyahar/python-dict-profiler)