the module itertools is collection of very powerful--and carefully designed--functions for performing iterator algebra that isthese allow you to combine iterators in sophisticated ways without having to concretely instantiate anything more than is currently required as well as the basic functions in the module itselfthe module documentation provides number of shortbut easy to get subtly wrongrecipes for additional functions that each utilize two or three of the basic functions in combination the third-party module more_itertools mentioned in the preface provides additional functions that are likewise designed to avoid common pitfalls and edge cases the basic goal of using the building blocks inside itertools is to avoid performing computations before they are requiredto avoid the memory requirements of large instantiated collectionto avoid potentially slow / until it is stricly requiredand so on iterators are lazy sequences rather than realized collectionsand when combined with functions or recipes in itertools they retain this property here is quick example of combining few things rather than the stateful fibonacci class to let us keep running sumwe might simply create single lazy iterator to generate both the current number and this sumdef fibonacci()ab while trueyield ab ba+ from itertools import teeaccumulate st tee(fibonacci()pairs zip(taccumulate( )for (fibtotalin zip(range( )pairs)print(fibtotal moduleitertools