Data Class Guides in Python >=3.10

dataclasses.py

import random
import string
from dataclasses import dataclass, field


def generate_id() -> str:
    return "".join(random.choices(string.ascii_uppercase, k=12))


"""
dataclass: 
- Frozen  = You cant change the class attributes once it is initialized
- kw_only = You have to mention the attributes in kw=value manner while initializing the class object like Person(name = "A") not Person("A")
- slots : Accessing object's attributes will be very fast
"""


@dataclass(frozen=False, kw_only=True, slots=True)
class Person:
    name: str
    address: str

    # we can also define default variables like "active"
    active: bool = True

    """
    Creating a default value other than boolean, we need to use
    the field function which takes in a `default_factory=func` func as 
    default factory that generates the deafault value
    """
    email_addresses: list[str] = field(default_factory=list)
    # here a new list is being generated for each instance of person

    # e.g of creating default values
    id: str = field(init=True, default_factory=generate_id)

    """
    you can also specify that an attribute can not be initialized by user so, 
        
        id:str = field(init=False, default_factory = generate_id)
    """

    # Printing the class attributes
    """
    This was the old way of printing the attributes of a class
    With dataclass this is not required
    
    def __str__(self)->str:
        return f"{self.name}, {self.address}"
    """

    # When you want to create other attributes using the attributes provides / initialized
    # We will generate the search string from the name and the address
    _search_string: str = field(init=False, repr=False)

    """
    Search string is something internal to the class like a private variable so it must be hidden, for that:
    1. We add the underscore before the variable 
    2. We assign repr=False
    """

    def __post_init__(self) -> None:
        self._search_string = f"{self.name} {self.address}"


if __name__ == "__main__":
    person = Person(name="Kamal Shrestha", address="123 Chelsea Street")

    """
    Default values can also be sent as an initialized values like
        person = Person(name="Kamal Shrestha", address="123 Chelsea Street", active=False)
    """

    print(person)
    
    # Person(name='Kamal Shrestha', address='123 Chelsea Street', active=True, email_addresses=[], id='JEVCOBQKFFBJ')