Is abstract class field in python possible?

When creating a Python class, is it a best practice to use one underscore or two when declaring class variables?

• class Example(object): __myClassVar = "A Class Var" or ... _myClassVar = "..." This is a question re:convention, the most used one by programmers.  Being Python already creates special methods with double underscores (e.g. __init__, __str__, etc.) I'd like to know if it's a best practice to use a single underscore to indicate a user defined class variable that maintains class name mangling.

• Answer:

  Short Answer : To use these attributes as private variables, the only way is to make their names start with two underscores and not letting their names end with two underscores. Long Answer : As a matter of fact, two underscores and one underscore is not the same at all. Nor is it a question of convention. A member or even method for that matter, when started with two underscores, will undergo name mangling. Exception being members and methods which both start and end with two underscores. As a rule of thumb : __attr_or_method_name : Can be used as private variables and methods. __attr_or_method_name__ : Generally used to implement special purpsose methods and it doesn't really make sense to come up with our own. _attr_or_method_name : just like any other attribute or method. The starting underscore doesn't make any difference whatsoever. class Example (object) : __private_var = "I am private" _just_another_var = "Nothing different" __special_purpose_var__ = "I don't know why I am special purpose" def __privateMethod (self) : pass def _yetAnotherMethod (self) : pass def __specialPurposeMothod__ (self) : pass example = Example () for attr in dir (example) : print attr And the relevant part, from what it prints, is this... _Example__privateMethod _Example__private_var __specialPurposeMothod__ __special_purpose_var__ _just_another_var _yetAnotherMethod As you can see, name mangling happens only when it starts with two underscores, but doesn't end with two underscores.