iterations and comprehensions in the prior we met python' two looping statementswhile and for although they can handle most repetitive tasks programs need to performthe need to iterate over sequences is so common and pervasive that python provides additional tools to make it simpler and more efficient this begins our exploration of these tools specificallyit presents the related concepts of python' iteration protocola methodcall model used by the for loopand fills in some details on list comprehensionswhich are close cousin to the for loop that applies an expression to items in an iterable because these tools are related to both the for loop and functionswe'll take two-pass approach to covering them in this bookalong with postscriptthis introduces their basics in the context of looping toolsserving as something of continuation of the prior revisits them in the context of function-based toolsand extends the topic to include built-in and user-defined generators also provides shorter final installment in this storywhere we'll learn about user-defined iterable objects coded with classes in this we'll also sample additional iteration tools in pythonand touch on the new iterables available in python --where the notion of iterables grows even more pervasive one note up frontsome of the concepts presented in these may seem advanced at first glance with practicethoughyou'll find that these tools are useful and powerful although never strictly requiredbecause they've become commonplace in python codea basic understanding can also help if you must read programs written by others