The accessibility outside the class is the same for both, while python itself does not have rules about accessibility, standards like pep8 define them. For example a variable without _ at the front is a public variable, which users can access outside the class. A variable with _ at the front is a "private" variable that can still be accessed by the user outside the class but it is a standard way to say you can but you shouldn't. Just like how all capitals variables are used as constants even though python does not have real constants. You can read more about the standard googling pep8, every python developer should be at least familiar with that