have some naming restrictions table - has examples of legal variable names you can name variable anything as long as it obeys the following three rulesit can be only one word with no spaces it can use only lettersnumbersand the underscore (_character it can' begin with number table - valid and invalid variable names valid variable names invalid variable names current_balance current-balance (hyphens are not allowedcurrentbalance current balance (spaces are not allowedaccount account (can' begin with number_ (can' begin with numbertotal_sum total_$um (special characters like are not allowedhello 'hello(special characters like are not allowedvariable names are case-sensitivemeaning that spamspamspamand spam are four different variables though spam is valid variable you can use in programit is python convention to start your variables with lowercase letter this book uses camelcase for variable names instead of underscoresthat isvariables looklikethis instead of looking_like_this some experienced programmers may point out that the official python code stylepep says that underscores should be used unapologetically prefer camelcase and point to the " foolish consistency is the hobgoblin of little mindssection in pep itselfconsistency with the style guide is important but most importantlyknow when to be inconsistent--sometimes the style guide just doesn' apply when in doubtuse your best judgment your first program while the interactive shell is good for running python instructions one at timeto write entire python programsyou'll type the instructions into the file editor the file editor is similar to text editors such as notepad or textmatebut it has some features specifically for entering source code to open new file in muclick the new button on the top row the window that appears should contain cursor awaiting your inputbut it' different from the interactive shellwhich runs python instructions python basics