Skip to content

Effortlessly Implementing Frozen Dataclasses in Python


Python Dataclasses: A Comprehensive Guide


Python dataclasses are a powerful feature introduced in Python 3.7 that simplifies the creation and management of classes used primarily for storing data. In this tutorial, we will explore the various aspects of dataclasses and learn how to use them effectively.

What are Dataclasses?

Dataclasses in Python are a convenient way to define classes that primarily serve as data containers. They provide a concise syntax for defining attributes, as well as automatic implementation of special methods such as __init__, __repr__, __eq__, and more. Dataclasses eliminate the need for boilerplate code, making it easier to write and read data-centric classes.

Creating a Dataclass

To create a dataclass, we need to import the dataclass decorator from the dataclasses module. Let’s see an example:

from dataclasses import dataclass
class Person:
name: str
age: int
city: str

In the above code, we define a Person dataclass with three attributes: name (a string), age (an integer), and city (a string). The dataclass decorator automatically generates special methods for the class, such as __init__, __repr__, etc.

Initializing Dataclass Instances

Since we defined the Person dataclass, we can now create instances of it. Let’s create a few Person objects:

person1 = Person("John Doe", 25, "New York")
person2 = Person("Jane Smith", 30, "San Francisco")
person3 = Person("Alice Johnson", 40, "Chicago")

We can access the attributes of a dataclass instance using the dot notation. For example:

print( # Output: John Doe
print(person2.age) # Output: 30
print( # Output: Chicago

Immutable Dataclasses

By default, dataclass attributes are mutable, meaning their values can be changed after initialization. However, if you want to create immutable dataclasses, you can use the frozen parameter of the dataclass decorator. Let’s see an example:

class Point:
x: int
y: int

With the frozen=True parameter, any attempt to modify the attributes of a Point instance will raise a dataclasses.FrozenInstanceError.

Comparison and Equality

Dataclasses provide automatic implementation of comparison and equality methods such as __eq__, __ne__, __lt__, and __gt__. These methods compare the attribute values of two instances and return the appropriate result. Let’s see an example:

class Fruit:
name: str
color: str
fruit1 = Fruit("Apple", "Red")
fruit2 = Fruit("Banana", "Yellow")
print(fruit1 == fruit2) # Output: False (different attributes)
fruit3 = Fruit("Apple", "Red")
print(fruit1 == fruit3) # Output: True (same attributes)

Nesting Dataclasses

Dataclasses can also be nested within each other, allowing the creation of complex data structures. Let’s see an example:

class Address:
street: str
city: str
class Person:
name: str
age: int
address: Address

In the above code, the Person dataclass contains an attribute address, which is an instance of the Address dataclass. This allows us to create hierarchical data structures easily.


Python dataclasses are a powerful tool for creating and managing data-centric classes. They eliminate the need for writing boilerplate code and provide automatic implementation of special methods. We covered the basics of creating dataclasses, initializing instances, making them immutable, and comparing them. Dataclasses are widely used in data science and other areas where efficient data management is crucial.