Python Special Attributes

Python has multiple special attributes that are defined per default for each class such as __name__, __module__, __dict__, __bases__, __doc__, and __annotations__.

Each of these special attributes has a special meaning as shown in the following table:

Let’s dive into a number of examples to show how these special attributes work.

Python Special Attribute __name__

Python’s special attribute __name__ is a string that defines the name of the class.

A minimal example can be seen in the interactive Python shell mode:

>>> __name__
'__main__'

The current name of the module in which this code runs is '__main__'.

If you would import a module with say import my_module and my_module would print(__name__), the result would be the name 'my_module' and not '__main__'.

Related Article:

• What Does “if __name__ == ‘__main__’” Do in Python?

Python Special Attribute __module__

Python’s special attribute __module__ prints the string name of the module where the class is defined.

Here’s an example:

class My_Class:
    def __init__(self):
        print(__name__)


My_Class().__module__
# __main__

For this example, I copied this code into a file 'code.py' and executed this code file as the main module. That’s why the output is '__main__'.

Python Special Attribute __dict__

Python’s special attribute __dict__ contains the dictionary with the namespace of the class. The dictionary maps the name of the attribute to its specific instantiation.

The following example shows the __dict__ contents of a custom class Person with two attributes name and age and their specific values 'alice' and 23, respectively.

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age


alice = Person('alice', 23)
print(alice.__dict__)
# {'name': 'alice', 'age': 23}

Python Special Attribute __bases__

Python’s special attribute contains a tuple with base classes of this class.

The following example defines a Child class with two parent classes Parent and Person. If you print the __bases__ attribute, it shows you a tuple with two references to these base classes:

class Parent:
    pass

class Person:
    pass

class Child(Parent, Person):
    pass


print(Child.__bases__)
# (<class '__main__.Parent'>, <class '__main__.Person'>)

Feel free to dive deeper into the concepts of OOP inheritance in our article:

• Five Types of Inheritance in Python

Python Special Attribute __doc__

Python objects have an attribute called __doc__ that provides a documentation of the object. For example, you simply call Dog.__doc__ on your class Dog to retrieve its documentation as a string.

class Dog:
    """Your best friend."""

    def do_nothing(self):
        pass


print(Dog.__doc__)
# Your best friend. 

More here:

• What is __ doc __ in Python?

Python Special Attribute __annotations__

Annotations are defined in PEP 3107 allow you to add arbitrary metadata to the parameters and return values of functions.

The __annotations__ attribute of a function object stores those annotations in a dictionary mapping function parameters or the return value to the specified annotations.

def save(x: "starting capital",
         y: "annual return (e.g., 0.1 == 10%)",
         n: "number of years"):
    return x * (1+y)**n

# Investing $10,000 at 10% for 50 years
print(save(10000, 0.1, 50))
# 1173908.5287969578
# = $1.1 million USD

You can print the annotations using the __annotations__ attribute of the function save:

print(save.__annotations__)
# {'x': 'starting capital', 'y': 'annual return (e.g., 0.1 == 10%)', 'n': 'number of years'}

More here:

• Python __annotations__ Attribute
• https://docs.python.org/3/reference/datamodel.html