fault value in scriptthe function xy may now be called in many different ways for exampleprint xy( would make xy perform the computations with and the default values ( zeroof and the two numbers returned from xy are printed to the screen if we wanted to use another initial value for ywe coulde write print xy( , = which would make xy perform the calculations with ( the default valueand when there are several positional argumentsthey have to appear in the same order as defined in the function definitionunless we explicitly use the names of these also in the function call with explicit name specification in the callany order of parameters is acceptable to illustratewe coulde call xy as print xy( = = = in any programming languageit is good habit to include little explanation of what the function is doingunless what is done by the function is obviouse when having only few simple code lines this explanation is called doc stringwhich in python should be placed just at the top of the function this explanation is meant for human who wants to understand the codeso it should say something about the purpose of the code and possibly explain the arguments and return values if needed if we do that with our xy function from abovewe may write the first lines of the function as def xy( xv yt)"""compute the and position of the ball at time ""note that other functions may be called from within other functionsand function input parameters are not required to be numbers any object will doe string variables or other functions functions are straightforwardly passed as arguments to other functionsas illustrated by the following script function_as_argument pydef sum_xy(xy)return def prod_xy(xy)return * def treat_xy(fxy)return (xyx print treat_xy(sum_xyxyprint treat_xy(prod_xyxy