introduction to python now we are ready to start learning some of the basic elements of python these are common to almost all programming languages in conceptthough not necessarily in detail the reader should be forewarned that this book is by no means comprehensive introduction to python we use python as vehicle to present concepts related to computational problem solving and thinking the language is presented in dribs and drabsas needed for this ulterior purpose python features that we don' need for that purpose are not presented at all we feel comfortable about not covering the entire language because there are excellent online resources describing almost every aspect of the language when we teach the course on which this book is basedwe suggest to the students that they rely on these free online resources for python reference material python is living language since its introduction by guido von rossum in it has undergone many changes for the first decade of its lifepython was little known and little used language that changed with the arrival of python in in addition to incorporating number of important improvements to the language itselfit marked shift in the evolutionary path of the language large number of people began developing libraries that interfaced seamlessly with pythonand continuing support and development of the python ecosystem became community-based activity python was released at the end of this version of python cleaned up many of the inconsistencies in the design of the various releases of python (often referred to as python xhoweverit was not backward compatible that meant that most programs written for earlier versions of python could not be run using implementations of python the backward incompatibility presents problem for this book in our viewpython is clearly superior to python howeverat the time of this writingsome important python libraries still do not work with python we willthereforeuse python (into which many of the most important features of python have been "back ported"throughout this book the basic elements of python python programsometimes called scriptis sequence of definitions and commands these definitions are evaluated and the commands are executed by the python interpreter in something called the shell typicallya new shell is created whenever execution of program begins in most casesa window is associated with the shell we recommend that you start python shell nowand use it to try the examples contained in the remainder of the andfor that matterlater in the book as well commandoften called statementinstructs the interpreter to do something for examplethe statement print 'yankees rule!instructs the interpreter to output the string yankees ruleto the window associated with the shell