cPython does alot of work for just about any piece of code. Just a small handful of things: 1. everything's a hash (object data, variable lookup, etc). jmoiron

cPython does alot of work for just about any piece of code. Just a small handful of things: 1. everything's a hash (object data, variable lookup, etc). jmoiron wrote a great article on the topic http://jmoiron.net/blog/whats-going-on/ http://jmoiron.net/blog/whats-going-on/ 2. refcounting introduces overhead for every variable access 3. loops are making all kinds of function calls to __iter__, next(), and catching StopIteration, which makes it hard to have a tight loop. 4. There's the GIL, builtin locking isn't great. 5. lots of indirection (lack of value types)