This deep dive has taken us from the fundamentals of classes to the advanced, powerful mechanisms that make Python's OOP model so unique and effective. We've seen how to use magic methods, enforce contracts with protocols, manage behavior with properties and descriptors, and even control class creation with metaclasses. By combining these tools with principles like SOLID and established design patterns, you will be able to create systems that are not only functional but also elegant, maintainable, and truly high-quality.
When you create a class, Python calls the metaclass's __new__ and __init__ methods to construct the class object. By creating a custom metaclass (a subclass of type ), you can intercept and customize the creation process.
s = Secret() print(s._Secret__private) # Accessible via mangled name # print(s.__private) # AttributeError
__del__ is called when the object’s reference count reaches zero. However, Python’s garbage collector (and circular references) makes __del__ unpredictable. in favor of context managers ( with ). python 3 deep dive part 4 oop high quality
class B: def (self): print("B init") super(). init ()
Use the abc module to force subclasses to implement specific methods. This checks for compatibility at instantiation.
By default, Python stores instance attributes in a dynamic dictionary ( __dict__ ). This allows flexibility but wastes memory. If you are instantiating millions of small objects, use __slots__ to white-list allowed attributes and eliminate __dict__ overhead. This deep dive has taken us from the
: __repr__ should be unambiguous, often eval -able. __str__ should be readable.
class ByePlugin(Plugin): def run(self): print("Bye")
class Pipeline: def (self): self._plugins: List[Plugin] = [] When you create a class, Python calls the
A double underscore triggers . Python changes the name of the variable to _ClassName__variable at compile time. This prevents accidental name collisions in subclasses, but it does not truly prevent access if someone tries hard enough.
While ABCs enforce contracts, they still require inheritance, which can sometimes be inflexible.
class Person: name = ValidString() # Using the descriptor