Underscore vs Double underscore with variables and methods

Single underscore

It is used before an object’s name to indicate other programmers that the method is meant to be private. It is also used in the name of methods which are fully intended to be overridden by subclasses. Ex- _abc

Double underscore

They are used for fully private methods. Ex- if your class is intended to be subclassed and you have attributes which you do not want the subclass to use, you can name them using a double underscore.

The rules of underscores in Python remain the same whether it is an object or a function, etc. Let us see an example of class for better understanding of the difference between the single and double underscores.

• _single_leading_underscore: weak "internal use" indicator. E.g.

  from M import *

  does not import objects whose name starts with an underscore.

• single_trailing_underscore_: used by convention to avoid conflicts with Python keyword, e.g.

  Tkinter.Toplevel(master, class_='ClassName')

• __double_leading_underscore: when naming a class attribute, invokes name mangling (inside class FooBar, __boo becomes _FooBar__boo; see below).

• __double_leading_and_trailing_underscore__: "magic" objects or attributes that live in user-controlled namespaces. E.g. __init__, __import__ or __file__. Never invent such names; only use them as documented.