type_guided_refactorings.py

from dataclasses import dataclass
from typing import List

@dataclass(frozen=True)
class Person:
  name: str
  age: int
  preferred_operating_systems: List[str]


@dataclass(frozen=True)
class Laptop:
  id: int
  manufacturer: str
  model: str
  screen_size_in_inches: float
  operating_system: str


def find_possible_laptops(laptops: List[Laptop], person: Person) -> List[Laptop]:
  possible_laptops = []
  for laptop in laptops:
    if laptop.operating_system in person.preferred_operating_systems:
      possible_laptops.append(laptop)
  return possible_laptops


people = [
  Person(name="Imran", age=22, preferred_operating_systems=["Ubuntu", "Arch Linux"]),
  Person(name="Eliza", age=34, preferred_operating_systems=["Arch Linux"]),
]

laptops = [
  Laptop(id=1, manufacturer="Dell", model="XPS", screen_size_in_inches=13, operating_system="Arch Linux"),
  Laptop(id=2, manufacturer="Dell", model="XPS", screen_size_in_inches=15, operating_system="Ubuntu"),
  Laptop(id=3, manufacturer="Dell", model="XPS", screen_size_in_inches=15, operating_system="ubuntu"),
  Laptop(id=4, manufacturer="Apple", model="macBook", screen_size_in_inches=13, operating_system="macOS"),
]

for person in people:
  possible_laptops = find_possible_laptops(laptops, person)
  print(f"Possible laptops for {person.name}: {possible_laptops}")


# I learned how type checking helps when refactoring code.
# Mypy shows exactly which parts of the code need to change when we rename or change a field type.
# This makes large codebases easier to update safely.