Python Dataclasses
Dataclasses are python classes, but are suited for storing data objects.
This module provides a decorator and functions for automatically adding generated special methods such as __init__() and __repr__() to user-defined classes.
Features
-
They store data and represent a certain data type. Ex: A number. For people familiar with ORMs, a model instance is a data object. It represents a specific kind of entity. It holds attributes that define or represent the entity.
-
They can be compared to other objects of the same type. Ex: A number can be greater than, less than, or equal to another number.
Python 3.7 provides a decorator dataclass that is used to convert a class into a dataclass.
>>> class Number:
... def __init__(self, val):
... self.val = val
...
>>> obj = Number(2)
>>> obj.val
# 2
with dataclass
>>> @dataclass
... class Number:
... val: int
...
>>> obj = Number(2)
>>> obj.val
# 2
Default values
It is easy to add default values to the fields of your data class.
>>> @dataclass
... class Product:
... name: str
... count: int = 0
... price: float = 0.0
...
>>> obj = Product("Python")
>>> obj.name
# Python
>>> obj.count
# 0
>>> obj.price
# 0.0
Type hints
It is mandatory to define the data type in dataclass. However, If you would rather not specify the datatype then, use typing.Any.
>>> from dataclasses import dataclass
>>> from typing import Any
>>> @dataclass
... class WithoutExplicitTypes:
... name: Any
... value: Any = 42