15. Python Descriptors (__get__, __set__) & @property Deep Dive • Python 0-to-Hero Mastery (Big Tech SDE & ML Standard) • Rishabh Ki Kaksha

Python 0-to-Hero Mastery (Big Tech SDE & ML Standard) › 15. Python Descriptors (__get__, __set__) & @property Deep Dive

45 mins

Course Syllabus

Module 1: Python Foundations & Virtual Machine Architecture

01. What is Python? History, CPython Architecture & PVM 02. Memory Management, Reference Counting & The GIL 03. Datatypes Deep Dive: Mutable vs Immutable & Integer Interning Cache 04. Dynamic Typing, Duck Typing & Python 3.12 Strict Type Hinting

Module 2: Flow Control, Collections & Functional Mastery

05. Variables, Scope & The LEGB Rule (Local, Enclosing, Global, Built-in) 06. Comprehensions & The Walrus Operator (:=) for High Performance 07. First-Class Functions, *args, **kwargs & Functional Combinators 08. Advanced Closures, Function Decorators & @functools.wraps

Module 3: Generators, Iterators & Memory-Safe Stream Processing

09. The Iterator Protocol (__iter__, __next__) & Generator Functions 10. Generator Pipelines & Infinite Stream Processing with itertools 11. Context Managers: The "with" Statement & contextlib.contextmanager

Module 4: Object-Oriented Python, Dunder Magic & Metaprogramming

15. Python Descriptors (__get__, __set__) & @property Deep Dive 16. Metaclasses: How Classes are Created (__new__ vs __init__) 12. Classes, Instances, Class Attributes & @classmethod vs @staticmethod 13. Dunder / Magic Methods Masterclass (__repr__, __call__, __getitem__) 14. Multiple Inheritance, MRO & C3 Linearization Algorithm (super())

Module 5: Concurrency, Multithreading & Asynchronous Programming

17. Concurrency Overview: CPU-Bound vs I/O-Bound Bottlenecks 18. Multithreading & ThreadPoolExecutor for High-Throughput I/O 19. Multiprocessing & ProcessPoolExecutor for CPU-Intensive Workloads 20. asyncio Event Loop Masterclass: Coroutines, Tasks & asyncio.gather

Module 6: Production Engineering, Testing & Performance Profiling

21. File I/O, Serialization (JSON, Pickle) & Pathlib Architecture 22. Robust Exception Hierarchies (try/except/else/finally) 23. Performance & Memory Profiling (cProfile, timeit & tracemalloc) 24. Production Package Architecture: pyproject.toml & Virtual Envs

Interactive Lesson Studio

# 15. Python Descriptors (__get__, __set__) & @property Deep Dive

> Python 0-to-Hero Notes by Rishabh - Topic 15

---

### 1. What are Descriptors? (The Engine Behind `@property`) ⚙️

Descriptor ek aisa object hai jo `__get__()`, `__set__()`, ya `__delete__()` methods implement karta hai:

```python
class PositiveNumber:
    def __set_name__(self, owner, name):
        self.name = name

def __get__(self, instance, owner):
        if instance is None: return self
        return instance.__dict__.get(self.name, 0)

def __set__(self, instance, value):
        if value <= 0:
            raise ValueError(f"{self.name} must be strictly positive!")
        instance.__dict__[self.name] = value

class BankAccount:
    balance = PositiveNumber() # Reusable Descriptor!
```

---

### 2. Data Descriptors vs Non-Data Descriptors

*   **Data Descriptor (Implements `__set__` or `__delete__`):** Instance dictionary (`instance.__dict__`) se higher precedence rakhta hai.
*   **Non-Data Descriptor (Implements only `__get__` e.g. methods):** Instance dictionary se lower precedence rakhta hai.

---

### 3. Interview Ke 3 Sawal Is Topic Se

1. **`__set_name__` method (PEP 487) descriptors me kya karta hai?** -> Class creation time par automatically attribute ka name (`'balance'`) capture karta hai.
2. **`@property` caching (`@functools.cached_property`) kaise kaam karti hai?** -> Pehle access par value compute karke `instance.__dict__` me write kar deti hai jisse subsequent accesses $O(1)$ fast dictionary lookups ban jate hain.
3. **ORM field validation (Django / SQLAlchemy) descriptors par kaise based hai?** -> Model columns (e.g. `models.CharField()`) actual me class-level descriptors hote hain jo database type casting handle karte hain.

---
**Next Topic:** 16. Metaclasses: How Classes are Created (__new__ vs __init__)

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1 Questions

Easy

1. Type-Enforced Integer Descriptor

Ek `TypedInteger` descriptor likhein jo non-integer value assign karne par `TypeError` throw kare.

💡 View Pro Interview Hint

• Use __set_name__ and __set__.

Python 3.12

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🎯 Big Tech Coding & Interview Challenges

1. Type-Enforced Integer Descriptor

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Rishabh Gehlot

PHP 8+ & Laravel 11 Master Track