common way to represent variables on paper is to write the name with an arrow pointing to the variable' value type(messagetype(ntype(pivariable names and keywordsprogrammers generally choose names for their variables that are meaningful they document what the variable is used for variable names can be arbitrarily long they can contain both letters and numbersbut they have to begin with letter it is legal to use uppercase lettersbut it is good idea to begin variable names with lowercase letter the underscore character_can appear in name it is often used in names with multiple wordssuch as my_name or airspeed_of_unladen_swallow if you give variable an illegal nameyou get syntax error mumbai'big citysyntaxerrorinvalid syntax more syntaxerrorinvalid syntax class 'advanced pythonsyntaxerrorinvalid syntax mumbai is illegal because it does not begin with letter moreis illegal because it contains an illegal characterbut what' wrong with classit turns out that class is one of python' keywords the interpreter uses keywords to recognize the structure of the programand they cannot be used as variable names python has lot of keywords the number keeps on growing with the new features coming in python python is the current version as of writing this book there are keywords in python release we can get the complete list of keywords using python interpreter help utility python help (helpkeywords