Python · OOP: Properties, Methods & Data Classes

Which magic methods must your custom container define so that len(c), c[k], c[k] = v, del c[k], for x in c, and x in c all work?

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More in OOP: Properties, Methods & Data Classes

What does this print? ``` class C: @property def area(self): return self.w * self.h c = C(); c.w, c.h = 3, 4 print(c.area) print(c.area()) ```

You expose a public attribute obj.temp and ship it. Later you need to reject negative values on write. Why is starting with @property from day one the safer call?

A class has @property def x with only a getter. What happens at obj.x = 5?

What does this print? ``` class A: @staticmethod def add(a, b): return a + b print(A.add(2, 3)) print(A().add(2, 3)) ```

What is printed? ``` class A: @classmethod def who(cls): return cls.__name__ class B(A): pass print(A.who(), B.who()) ```

You want Date.from_string("2026-06-27") to build and return a Date instance (an alternative constructor). Which method kind, and what's the key line in the body?

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