This succinct, straightforward article shows you how to set default values in a dataclass in Python.
Setting Default Values in Dataclass
To set default values in a dataclass, we can use simple syntax like a variable declaration or use the default parameter in the field() function. The example below define a class called Person with 3 fields: name, age (default is 18), and city (default is Sling Academy):
from dataclasses import dataclass, field
@dataclass
class Person:
name: str
age: int = 18
city: str = field(default='Sling Academy')
# Create an instance of the class without providing age and city
person = Person('Foo Bar')
print(person)Output:
Person(name='Foo Bar', age=18, city='Sling Academy')Using the default_factory Parameter for Dynamic Default Values
There might be cases where we may need to set dynamic default values for a field in a dataclass. In such cases, we can use the default_factory parameter instead of default. default_factory must be a zero-argument callable that will be called when a default value is needed.
In the example below, we will define a class named Product with 3 fields: name, price (the default value is a random number between 900 and 1100), and production_year (the default value is the current year):
from datetime import datetime
from dataclasses import dataclass, field
from random import randint
# Get the current year
# Used to to set default value for production_year
def get_current_year():
return datetime.now().year
@dataclass
class Product:
name: str
price: float = 1000 + randint(-100, 100)
production_year: int = field(default_factory=get_current_year)
# Test code
product = Product('Blue Robot')
print(product)Output:
Product(name='Blue Robot', price=1091, production_year=2023)Afterword
Through the tutorial, we have learned how to set default values for fields in a dataclass. We have also seen how to use the default_factory parameter for dynamic default values. The examples, although simple, can give you a deep understanding of the topic. If you have any questions, leave comments. We will respond as soon as possible.
