Python: Private variables

To make Python treat a variable as pseudo-private, follow the convention of putting two underscores (i.e., __) at the beginning of the variable’s name, e.g.:

class Enki:
    def __init__(self):
        self.__private = 3.14
        print(self.__private)

enki = Enki()  # prints 3.14

In effect, Python renames the variable using the _classname__varname pattern. If we try to access the original __private variable name, an error is thrown:

>>> print(enki.__private)
AttributeError .. no __private attribute

It is possible to access it through _classname__varname, but it’s not recommended to access variables in this way, because it is an implementation detail and may break in the future.

>>> print(enki._Enki__private)
prints 3.14

Update:

The double underscore (__) is primarily used for “name mangling” to ensure that subclasses don’t have overlapping methods. A single underscore (_) is a convention so that anyone looking at the code will know that it’s an implementation-specific attribute. As a handy side effect, from package import * won’t import attributes starting with underscores.

Via enkipro.com.