and an important part of programming 've added them to most of this book' examples to help explain the code in the next part of the bookwe'll meet related but more functional feature--documentation strings--that attaches the text of your comments to objects so it' available after your code is loaded because code you type interactively is temporarythoughyou won' normally write comments in this context if you're working alongthis means you don' need to type any of the comment text from the through to the end of the lineit' not required part of the statements we're running this way nowlet' use our new integer objects in some expressions at this pointthe values of and are still and respectively variables like these are replaced with their values whenever they're used inside an expressionand the expression results are echoed back immediately when we're working interactivelya ( ( * ( * ( addition ( )subtraction ( multiplication ( )division ( modulus (remainder)power ( * mixed-type conversions technicallythe results being echoed back here are tuples of two values because the lines typed at the prompt contain two expressions separated by commasthat' why the results are displayed in parentheses (more on tuples laternote that the expressions work because the variables and within them have been assigned values if you use different variable that has not yet been assignedpython reports an error rather than filling in some default valuec traceback (most recent call last)file ""line in nameerrorname 'cis not defined you don' need to predeclare variables in pythonbut they must have been assigned at least once before you can use them in practicethis means you have to initialize counters to zero before you can add to theminitialize lists to an empty list before you can append to themand so on here are two slightly larger expressions to illustrate operator grouping and more about conversionsand preview difference in the division operator in python and xb ( same as (( [use in xsame as ( ( )[use print before in the first expressionthere are no parenthesesso python automatically groups the components according to its precedence rules--because is lower in table - than numeric types