A Data Class smell occurs when a class does not implement enough functionality itself to justify it being a class.
This means that the class defines instance variables, but lacks relevant methods. Such classes are very likely being manipulated by other classes heavily.
from math import sqrt # Smelly code class Coordinates: def __init__(self, x_coordinate, y_coordinate, z_coordinate): self.x_coordinate = x_coordinate self.y_coordinate = y_coordinate self.z_coordinate = z_coordinate my_coordinates = Coordinates(4, -7, 43) print(sqrt(my_coordinates.x_coordinate**2 + my_coordinates.y_coordinate**2 + my_coordinates.z_coordinate**2)) # Pythagorean theorem # Fixed code class Coordinates: def __init__(self, x_coordinate, y_coordinate, z_coordinate): self.x_coordinate = x_coordinate self.y_coordinate = y_coordinate self.z_coordinate = z_coordinate def distance(self): return sqrt(self.x_coordinate**2 + self.y_coordinate**2 + self.z_coordinate**2) # Pythagorean theorem my_coordinates = Coordinates(4, -7, 43) print(my_coordinates.distance())
Often, this is an indication that relevant functionality for the data that it stores is being implemented elsewhere in the code, or that the data stored in objects of the class should be stored in another class.
To avoid this code smell, ensure that relevant functionality for the data is being stored in methods in the class, and that the data is being stored in the class which is most appropriate for it.
Books about code smells
Learn to write better smelling code.
Refactoring: Improving the Design of Existing Code
Code smells: A Predictor of Remarkable Quality Improvement
Clean Code: A Handbook of Agile Software Craftsmanship