Classes and Objects (Mental Model)

Model domain concepts with classes, keep state explicit, and design objects that reduce coupling in production code.

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Why Objects

Objects help you bundle data with behavior and define boundaries. In production, boundaries reduce accidental complexity and make failures easier to isolate.

Minimal Class

class RateLimiter:
    def __init__(self, limit: int) -> None:
        self.limit = limit
        self.count = 0

    def allow(self) -> bool:
        self.count += 1
        return self.count <= self.limit

Operational Checklist

Classes represent domain concepts, not random bags of functions.
State is explicit and initialized in __init__.
Public methods form a small, intentional API.

Failure Modes

God object: one class accumulates unrelated responsibilities.
Hidden state: behavior depends on implicit globals or module-level caches.

__init__ and Instance State →