Breaching outside of Python 101 books and guides, you might’ve stumbled across data classes that look something like this:
from dataclasses import dataclass
@dataclass
class User:
name: str
age: intWhat is a data class?
A data class is a Python decorator that allows us to write code that generates common special (“dunder”) methods for a class based on its type-annotated fields. You define the data structure using type annotations and the @dataclass decorator uses that structure to create your class.
» Dunder (“double underscore”) methods are special methods that are intended to be used internally to the class like object construction (__init__), comparison (__eq__, __lt__, __gt__, etc.), and more.
In short, these classes allow you to write less boilerplate code and communicate clearer intent of the class.
Why would we use a data class?
Let’s take a scenario where you’re writing a class to hold weather observations. You might write it like this:
class WeatherObservation:
def __init__(
self,
temperature: float,
dewpoint: float,
wind_speed: float,
wind_direction: int
):
self.temperature = temperature
self.dewpoint = dewpoint
self.wind_speed = wind_speed
self.wind_direction = wind_directionWhile there isn’t anything wrong with the code, we can simplify the code to use a data class instead, which automatically sets your data type and class values:
from dataclasses import dataclass
@dataclass
class WeatherObservation:
temperature: float
dewpoint: float
wind_speed: float
wind_direction: intHowever, a weather observation class most likely will need to hold more variables like pressure. So, instead of adding pressure: float to the arguments and self.pressure = pressure in the __init__ method above, we can just add pressure: float to our data class instead.
When would we use a data class?
In practice, there’s a few different places where we’d use data classes:
Configuration objects: applications need structured configurations loaded from environment variables or remote services.
Data-centric modeling: for internal concepts (like a weather observation), you’ll be able to communicate what the object represents
Structured return values: Sometimes, returning a dictionary or a tuple might be too much - a data class offers that “source of truth” and a clear interface as to what’s being returned.
Happy coding!
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