Python class methods, static methods, and properties

Special Method Types

Python has three method types. Instance methods receive self. Class methods receive the class (cls). Static methods receive neither — they are plain functions scoped to the class namespace.

class Circle:
    PI = 3.14159

    def __init__(self, radius):
        self._radius = radius

    @property
    def radius(self):
        return self._radius

    @radius.setter
    def radius(self, value):
        if value < 0:
            raise ValueError("Radius must be non-negative")
        self._radius = value

    @classmethod
    def from_diameter(cls, diameter):
        return cls(diameter / 2)

    @staticmethod
    def is_valid_radius(r):
        return r > 0

c = Circle.from_diameter(10)
print(c.radius)          # 5.0
c.radius = 7
print(Circle.is_valid_radius(-1))  # False

Properties

A @property turns a method into a computed attribute with controlled access. Add a @name.setter to allow assignment with validation. This is the Pythonic alternative to Java-style get/set methods.

Properties enforce encapsulation without the verbose getter/setter boilerplate common in Java. They let you add validation, caching, or computation to what looks like a plain attribute access from the outside. If you later need to add validation to a public attribute, you can convert it to a property without changing the calling code — this is why Python code starts with public attributes rather than defensive getters. Use a leading underscore (_attr) to signal an attribute is internal by convention, and a double underscore (__attr) to trigger name mangling.