Source: https://realpython.com/python-getter-setter/

A simple example

# employee.py

from datetime import date

class Employee:
    def __init__(self, name, birth_date, start_date):
        self.name = name
        self.birth_date = birth_date
        self.start_date = start_date

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value.upper()

    @property
    def birth_date(self):
        return self._birth_date

    @birth_date.setter
    def birth_date(self, value):
        self._birth_date = date.fromisoformat(value)

    @property
    def start_date(self):
        return self._start_date

    @start_date.setter
    def start_date(self, value):
        self._start_date = date.fromisoformat(value)

Refactored: using descriptor

# employee.py

from datetime import date

class Date:
    def __set_name__(self, owner, name):
        self._name = name

    def __get__(self, instance, owner):
        return instance.__dict__[self._name]

    def __set__(self, instance, value):
        instance.__dict__[self._name] = date.fromisoformat(value)

class Employee:
    birth_date = Date()
    start_date = Date()

    def __init__(self, name, birth_date, start_date):
        self.name = name
        self.birth_date = birth_date
        self.start_date = start_date

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value.upper()

The .__setattr__() and .__getattr__() Methods

# point.py

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __getattr__(self, name: str):
        return self.__dict__[f"_{name}"]

    def __setattr__(self, name, value):
        self.__dict__[f"_{name}"] = float(value)

>>> from point import Point

>>> point = Point(21, 42)

>>> point.x
21.0
>>> point.y
42.0

>>> point.x = 84
>>> point.x
84.0

>>> dir(point)
['__class__', '__delattr__', ..., '_x', '_y']