variable names and keywords programmers generally choose names for their variables that are meaningful and document what the variable is used for variable names can be arbitrarily long they can contain both letters and numbersbut they cannot start with number it is legal to use uppercase lettersbut it is good idea to begin variable names with lowercase letter (you'll see why laterthe underscore character can appear in name it is often used in names with multiple wordssuch as my_name or airspeed_of_unladen_swallow variable names can start with an underscore characterbut we generally avoid doing this unless we are writing library code for others to use if you give variable an illegal nameyou get syntax error trombones 'big paradesyntaxerrorinvalid syntax more syntaxerrorinvalid syntax class 'advanced theoretical zymurgysyntaxerrorinvalid syntax trombones is illegal because it begins with number 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 reserves keywordsand as assert break class continue def del elif else except false finally for from global if import in is lambda none nonlocal not or pass raise return true try while with yield async await you might want to keep this list handy if the interpreter complains about one of your variable names and you don' know whysee if it is on this list statements statement is unit of code that the python interpreter can execute we have seen two kinds of statementsprint being an expression statement and assignment when you type statement in interactive modethe interpreter executes it and displays the resultif there is one