Not only is it slightly faster but you also avoid storing the entire list in memory! Actually that won't help when you need a big list and need to store it

Not only is it slightly faster but you also avoid storing the entire list in memory! Actually that won't help when you need a big list and need to store it in memory. Python is really akward with this kind of scenario. Doing calkulations with Maps of Lists is definitiv (extremly) faster in the JVM, C++ whatever. Python is good however some use cases are definitv not in favor of Python. I mean some could drop to C/C++ for that and pass Pointers around so not the biggest problem.