@property / @classmethod / @staticmethod

class MyClass:
    # Property (getter)
    @property
    def attr_name(self):
        return self._attr_name

    # Property (setter)
    @attr_name.setter
    def attr_name(self, value):
        self._attr_name = value

    # Class method (cls = the class itself)
    @classmethod
    def class_method(cls, arg):
        ...

    # Static method (no self or cls needed)
    @staticmethod
    def static_method(arg):
        ...

property_classmethod_1.py

class Temperature:
    def __init__(self, celsius):
        self._celsius = celsius

    @property
    def celsius(self):
        return self._celsius

    @celsius.setter
    def celsius(self, value):
        if value < -273.15:
            raise ValueError("Cannot set a temperature below absolute zero.")
        self._celsius = value

    @property
    def fahrenheit(self):
        return self._celsius * 9 / 5 + 32

t = Temperature(100)
print(t.celsius)
print(t.fahrenheit)

t.celsius = 0
print(t.fahrenheit)

try:
    t.celsius = -300
except ValueError as e:
    print(e)

Running the code produces the following output:

python3 property_classmethod_1.py
100
212.0
32.0
Cannot set a temperature below absolute zero.

property_classmethod_2.py

class User:
    _count = 0

    def __init__(self, name, email):
        self.name = name
        self.email = email
        User._count += 1

    @classmethod
    def get_count(cls):
        return cls._count

    @classmethod
    def from_dict(cls, data):
        return cls(data['name'], data['email'])

u1 = User('Gojo Satoru', 'gojo_satoru@wp-p.info')
u2 = User.from_dict({'name': 'Itadori Yuji', 'email': 'itadori_yuji@wp-p.info'})
print(User.get_count())
print(u1.name, u1.email)
print(u2.name, u2.email)

Running the code produces the following output:

python3 property_classmethod_2.py
2
Gojo Satoru gojo_satoru@wp-p.info
Itadori Yuji itadori_yuji@wp-p.info

property_classmethod_3.py

class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email

    @staticmethod
    def is_valid_email(email):
        return '@' in email and '.' in email

print(User.is_valid_email('gojo_satoru@wp-p.info'))
print(User.is_valid_email('invalid'))

u = User('Fushiguro Megumi', 'fushiguro_megumi@wp-p.info')
print(u.is_valid_email(u.email))

Running the code produces the following output:

python3 property_classmethod_3.py
True
False
True

Common Mistake 1: Directly modifying a private variable without @property

Variables prefixed with an underscore (e.g., _celsius) signal "private" by Python convention, but the language provides no real enforcement. Directly modifying them bypasses any validation defined in a setter.

mistake1_ng.py

class Temperature:
    def __init__(self, celsius):
        self._celsius = celsius

t = Temperature(100)
t._celsius = -999
print(t._celsius)

Running the code produces the following output:

python3 mistake1_ng.py
-999

mistake1_ok.py

class Temperature:
    def __init__(self, celsius):
        self._celsius = celsius

    @property
    def celsius(self):
        return self._celsius

    @celsius.setter
    def celsius(self, value):
        if value < -273.15:
            raise ValueError("Cannot set a temperature below absolute zero.")
        self._celsius = value

t = Temperature(100)
try:
    t.celsius = -999
except ValueError as e:
    print(e)

Running the code produces the following output:

python3 mistake1_ok.py
Cannot set a temperature below absolute zero.

Common Mistake 2: Choosing the wrong decorator between @classmethod and @staticmethod

Use @classmethod when the method needs access to the class itself (via cls). Use @staticmethod when the method uses neither the class nor any instance state. A @staticmethod cannot access the class through cls.

class User:
    _count = 0

    def __init__(self, name):
        self.name = name
        User._count += 1

    @staticmethod
    def get_count():
        return User._count

u1 = User('Gojo Satoru')
u2 = User('Itadori Yuji')
print(User.get_count())

mistake2_ok.py

class User:
    _count = 0

    def __init__(self, name):
        self.name = name
        User._count += 1

    @classmethod
    def get_count(cls):
        return cls._count

u1 = User('Gojo Satoru')
u2 = User('Itadori Yuji')
print(User.get_count())

Running the code produces the following output:

python3 mistake2_ok.py
2

Using @property lets you automatically add validation or conversion logic whenever an instance variable is accessed. Even if you change the internal implementation of a class, external code can still access it using the same property syntax, making it easier to maintain API compatibility.

@classmethod is frequently used as an alternative constructor (factory method). A common pattern is defining a from_dict() method that creates an instance from a dictionary or JSON data.

@staticmethod is used for logic that belongs to the class conceptually but does not use any class or instance state. If a method uses neither self nor cls, marking it as a staticmethod makes it clear that it belongs in the class scope rather than outside the class. Use @classmethod when you need access to the class itself, and @staticmethod when you do not.