Expert Python Programming - Second Edition

Advanced attribute access patterns

When many C++ and Java programmers first learn Python, they are surprised by Python's lack of a private keyword. The nearest concept is name mangling. Every time an attribute is prefixed by __, it is renamed by the interpreter on the fly:

class MyClass:
    __secret_value = 1

Accessing the __secret_value attribute by its initial name will raise an AttributeError exception:

>>> instance_of = MyClass()
>>> instance_of.__secret_value
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'MyClass' object has no attribute '__secret_value'
>>> dir(MyClass)
['_MyClass__secret_value', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', ...