GadaaLabs
Python Mastery — From Zero to AI Engineering
Lesson 5

Object-Oriented Programming — From Classes to Protocols

38 min

Part 1: Classes from Scratch

The Class Statement and __init__

A class is a blueprint for objects. When you call MyClass(), Python allocates a new instance (__new__), then calls __init__ to initialize it. self is not a keyword — it is simply the first parameter of every instance method, and Python automatically passes the instance as that first argument.

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Instance vs Class Attributes

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classmethod and staticmethod

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Part 2: Dunder (Magic) Methods

__repr__ and __str__

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Comparison Operators and @total_ordering

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Arithmetic Operators and Reflected Methods

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Container Protocol

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Context Manager, __call__, __bool__, and __slots__

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Part 3: Inheritance and MRO

Single Inheritance and super()

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Method Resolution Order (MRO) — C3 Linearization

Python uses the C3 linearization algorithm to compute the MRO. The invariant: a class always appears before its parents, and if two classes share an ancestor, the one listed first in the inheritance list takes precedence. This guarantees the ancestor is called exactly once in the diamond problem.

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Part 4: Properties and Descriptors

Properties — Controlled Attribute Access

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Descriptors — The Engine Behind Properties

Any class defining __get__, __set__, or __delete__ is a descriptor. Properties, classmethods, and staticmethods are all descriptors under the hood. Writing your own descriptor lets you reuse validation logic across multiple classes.

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Part 5: Abstract Classes and Protocols

ABC — Enforced Interfaces

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typing.Protocol — Structural Subtyping

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Part 6: Dataclasses

@dataclass — Auto-generated Boilerplate

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__post_init__, frozen, and inheritance

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Part 7: Advanced OOP Patterns

Metaclasses and __init_subclass__

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Observer Pattern

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Project: Bank Account System

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Exercises

Easy

1. Immutable Point3D

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2. StringBuilder

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Medium

3. Cached Property Descriptor

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4. Type-checked Model

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Hard

5. Decorator-based Event Handling

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6. Unit Conversion Descriptors

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7. Composable Pipeline

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8. Abstract Shape Registry

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