hello python worldhello python crash course worldyou can change the value of variable in your program at any timeand python will always keep track of its current value naming and using variables when you're using variables in pythonyou need to adhere to few rules and guidelines breaking some of these rules will cause errorsother guidelines just help you write code that' easier to read and understand be sure to keep the following variable rules in mindvariable names can contain only lettersnumbersand underscores they can start with letter or an underscorebut not with number for instanceyou can call variable message_ but not _message spaces are not allowed in variable namesbut underscores can be used to separate words in variable names for examplegreeting_message worksbut greeting message will cause errors avoid using python keywords and function names as variable namesthat isdo not use words that python has reserved for particular programmatic purposesuch as the word print (see "python keywords and built-in functionson page variable names should be short but descriptive for examplename is better than nstudent_name is better than s_nand name_length is better than length_of_persons_name be careful when using the lowercase letter and the uppercase letter because they could be confused with the numbers and it can take some practice to learn how to create good variable namesespecially as your programs become more interesting and complicated as you write more programs and start to read through other people' codeyou'll get better at coming up with meaningful names note the python variables you're using at this point should be lowercase you won' get errors if you use uppercase lettersbut it' good idea to avoid using them for now avoiding name errors when using variables every programmer makes mistakesand most make mistakes every day although good programmers might create errorsthey also know how to respond to those errors efficiently let' look at an error you're likely to make early on and learn how to fix it variables and simple data types