as the answer usually involves extensive knowledge of the application area we will therefore limit our testing to the verification part input data computer programs need set of input data and the purpose is to use these data to compute output datai results in the previous program we have specified input data in terms of variables howeverone often wants to get the input through some dialog with the user here is one example where the program asks questionand the user provides an answer by typing on the keyboardage input('what is your age'print "okso you're half way to %dwow!(age* soafter having interpreted and run the first linepython has established the variable age and assigned your input to it the second line combines the calculation of twice the age with message printed on the screen try these two lines in little test program to see for yourself how it works the input function is useful for numberslists ()and tuples (for pure textthe user must either enclose the input in quotesor the program must use the raw_input function insteadname raw_input('what is your name'there are other ways of providing input to program as welle via graphical interface (as many readers will be used toor at the command line ( as parameters succeedingon the same linethe command that starts the programreading data from file is yet another way logicallywhat the program produces when rune plot or printout to the screen or fileis referred to as program output symbolic computations even though the main focus in this book is programming of numerical methodsthere are occasions where symbolic (also called exact or analyticaloperations are useful doing symbolic computations meansas the name suggeststhat we do computations with the symbols themselves rather than with the numerical values they could represent let us illustrate the difference between symbolic and numerical computations with little example numerical computation could be * print which will make the number appear on the screen symbolic counterpart of this code could be