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What does the @property decorator do, and how does it let a method be accessed like an attribute? How do you add a setter to a property so assignment (obj.attr = value) triggers custom logic, like validation? How would you convert an existing plain attribute into a property later, without breaking any existing code that reads or writes it directly? What is a descriptor, and which dunder methods define the descriptor protocol? How does __set_name__ let a descriptor automatically learn the attribute name it's being assigned to on the owning class? How would you implement a lazy, cached property using a custom descriptor (or functools.cached_property) that only computes its value once? How do you write a descriptor that behaves differently when accessed on the CLASS itself versus on an INSTANCE? How would you implement a type-validating descriptor that enforces a specific type constraint, reusable across multiple attributes and classes? How does Python's own implementation of instance methods use the descriptor protocol to achieve automatic 'self' binding? How do you implement a descriptor-based ORM-style field that lazily loads related data only when actually accessed?
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What is the difference between a data descriptor and a non-data descriptor, and how does this affect attribute lookup priority?

Intermediate

Answer

A DATA descriptor implements BOTH __get__ AND __set__ (or __delete__); a NON-DATA descriptor implements ONLY __get__. Data descriptors take priority OVER an instance's __dict__ during attribute lookup, while non-data descriptors are OVERRIDDEN by an instance's __dict__ if the same name exists there — this priority difference is exactly how @property (a data descriptor) always wins even if you try to shadow it in self.__dict__.
class NonDataDescriptor:
    def __get__(self, instance, owner):
        return "from descriptor"

class Example:
    attr = NonDataDescriptor()

e = Example()
e.__dict__["attr"] = "from instance dict"
print(e.attr)  # 'from instance dict' -- instance __dict__ wins for non-data descriptors
Real-world example Understanding why a @property (data descriptor) can't be silently overridden by setting self.__dict__['prop_name'] directly.

Common follow-ups: Why does a functions themselves (used for bound methods) behave as a non-data descriptor?

Magic Methods & Operator Overloading
All 15 Descriptors & Properties questions