Challenge 2: Rectangle with @property — Possible Solution
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class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    @property
    def area(self):
        return self.width * self.height

r = Rectangle(5, 3)
print(r.area)

Output:
15

WHY THIS WORKS AS AN ANSWER
------------------------------
__init__(self, width, height) reuses the plain instance-attribute
pattern from Course 2, Chapter 1 — self.width and self.height are
stored directly, no computation involved yet.

@property above def area(self): reuses the chapter's own Circle class
example exactly — decorating a method with @property makes it
accessible as r.area rather than r.area(), even though it's really
running a small calculation (self.width * self.height) every time
it's read, not just returning a stored value.

Because area is never stored as its own instance attribute — it's
computed fresh from self.width and self.height on every access — it
can never drift out of sync with those two values the way a manually
cached area = width * height field set once in __init__ could if
width or height changed later. This is exactly the "value that's
always derived from other attributes" use case the chapter's Circle
example was built to demonstrate, just with multiplication instead of
the circle-area formula.