What are Python function attributes?

In Python, everything is an object, and functions are no exception. Since functions are objects, they can have attributes ? custom data attached to them, just like attributes on a class instance. This allows you to store metadata, counters, configuration, or any arbitrary data directly on a function.

Function attributes are different from function parameters. Parameters are inputs passed during a function call, while attributes are persistent data stored on the function object itself.

Syntax

You can set and access function attributes using the dot (.) operator, or using setattr() and getattr() built-in functions −

# Using dot operator
function_name.attribute = value
print(function_name.attribute)

# Using setattr / getattr
setattr(function_name, 'attribute', value)
print(getattr(function_name, 'attribute'))

To view all custom attributes on a function, use function_name.__dict__, which returns a dictionary of all user-defined attributes and their values.

Setting Attributes Inside a Function

In the below program, we define an attribute directly inside the function body, and set another attribute externally after calling the function −

Example

def function():
   function.a = 14
   print(function.a)

function()
function.name = "bar"
print(function.__dict__)

The output of the above code is −

14
{'a': 14, 'name': 'bar'}

The attribute a is set inside the function when it runs, while name is set externally. Both appear in the function's __dict__.

Using setattr() and getattr()

In the below program, we define an empty function and then add attributes using setattr(). We retrieve them using both getattr() and the dot operator −

Example

def city():
   pass

setattr(city, 'Name', 'Hyderabad')
setattr(city, 'State', 'Telangana')

print(getattr(city, 'Name'))
print(city.Name)
print(city.State)

The output of the above code is −

Hyderabad
Hyderabad
Telangana

setattr() and getattr() are useful when attribute names are dynamic (stored in variables) rather than hardcoded.

Mixing Attributes with Dot Operator and setattr()

Example

def foo():
   pass

setattr(foo, 'age', 23)
setattr(foo, 'name', 'John Doe')
foo.gender = 'male'

print(getattr(foo, 'age'))
print(foo.gender)
print(foo.name)
print(foo.__dict__)

The output of the above code is −

23
male
John Doe
{'age': 23, 'name': 'John Doe', 'gender': 'male'}

Both methods ? dot operator and setattr() ? store attributes in the same __dict__ dictionary on the function object.

Built-in Function Attributes

Every Python function comes with several built-in attributes by default −

Example

def greet(name="World"):
   """A simple greeting function"""
   return f"Hello, {name}!"

print("Name:", greet.__name__)
print("Docstring:", greet.__doc__)
print("Defaults:", greet.__defaults__)
print("Module:", greet.__module__)

The output of the above code is −

Name: greet
Docstring: A simple greeting function
Defaults: ('World',)
Module: __main__

Conclusion

Python functions are objects and can carry custom attributes set via the dot operator or setattr(). These attributes persist on the function object and can be retrieved using dot access, getattr(), or __dict__. Every function also has built-in attributes like __name__, __doc__, and __defaults__ that provide metadata about the function itself.