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focuses on mastering the Object-Oriented Programming paradigm to write robust, maintainable, and "high-quality" code . This stage of learning moves beyond basic class syntax and explores the internal machinery of Python objects.
class SingletonMeta(type): _instances = {} def __call__(cls, *args, **kwargs): if cls not in cls._instances: cls._instances[cls] = super().__call__(*args, **kwargs) return cls._instances[cls]
class Account: def __init__(self, owner, balance): self.owner = owner # Public self._tier = "Gold" # Protected self.__balance = balance # Private (mangled) acc = Account("Alice", 5000) # print(acc.__balance) # Raises AttributeError print(acc._Account__balance) # Works, but highly discouraged! Use code with caution. Properties vs. Getters/Setters python 3 deep dive part 4 oop high quality
class InventoryItem: # Descriptors handle the heavy lifting cleanly stock = IntegerField(min_value=0, max_value=1000) price = IntegerField(min_value=1) def __init__(self, name, stock, price): self.name = name self.stock = stock self.price = price Use code with caution.
class InMemoryUserRepository(UserRepository): def (self): self._users: dict[int, User] = {} def get_by_id(self, id: int) -> Optional[User]: return self._users.get(id) def save(self, user: User) -> None: self._users[user.id] = user
The magic of Python objects lies in "dunder" (double underscore) methods. These allow objects to integrate seamlessly with the language's syntax. Use code with caution
By default, Python stores instance attributes in a __dict__ — flexible but memory-hungry. __slots__ tells Python to use a fixed array.
: A strong hint to developers that the attribute is intended for internal use. It is not enforced by the interpreter.
: Deep knowledge of scopes, namespaces, closures, and decorators. Advanced Iteration : Deep knowledge of scopes
class Point: def __init__(self, x, y): self.x = x self.y = y # Each instance has a __dict__ (~72 bytes overhead + per attr)
: Distinguishing between instance, class, and static methods, and when to use each effectively.
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