Which convention is used in Python to indicate that methods and variables in a class are private and not to be used outside of the class?

Which convention is used in Python to indicate that methods and variables in a class are private and not to be used outside of the class?

• by using a single preceding underscore ( _ ) for a method or variable
• by using the command class private classname() : to start the class definition
• by using two preceding hyphens ( — ) for a method or variable
• by declaring a private method or variable in the beginning of the class definition