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: automatically generates __init__ and __repr__ methods
from dataclasses import dataclass
@dataclass # Decorator converts class to dataclass
class Number:
val: int # Type annotation required
obj = Number(2) # __init__ automatically created
obj.val
2
Default values
It is easy to add default values to the fields of your data class.
# Dataclass with default values: fields with defaults must come after required fields
@dataclass
class Product:
name: str # Required field
count: int = 0 # Optional field with default value
price: float = 0.0 # Optional field with default value
obj = Product("Python") # Only name required, others use defaults
obj.name
Python
obj.count
0
obj.price
0.0
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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