05. Variables, Scope & The LEGB Rule (Local, Enclosing, Global, Built-in) • Python 0-to-Hero Mastery (Big Tech SDE & ML Standard) • Rishabh Ki Kaksha

Python 0-to-Hero Mastery (Big Tech SDE & ML Standard) › 05. Variables, Scope & The LEGB Rule (Local, Enclosing, Global, Built-in)

45 mins

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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

# 05. Variables, Scope & The LEGB Rule (Local, Enclosing, Global, Built-in)

> Python 0-to-Hero Notes by Rishabh - Topic 05

---

### 1. The LEGB Scope Resolution Order 🔍

Python me jab kisi variable name ko access kiya jata hai, toh Python strictly is order me search karta hai:

```
[ L: Local Scope ] ➔ (Inside current function)
        ⬇
[ E: Enclosing Scope ] ➔ (Inside outer enclosing / nested functions)
        ⬇
[ G: Global Scope ] ➔ (Top-level of current module / file)
        ⬇
[ B: Built-in Scope ] ➔ (Python built-in functions: len, range, print)
```

---

### 2. `global` vs `nonlocal` Keywords

```python
x = "Global"

def outer():
    x = "Enclosing"
    def inner():
        nonlocal x # Modifies outer()'s variable, NOT global x!
        x = "Modified by Inner"
    inner()
    print("Outer x:", x) # Outputs: Modified by Inner

outer()
```

---

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

1. **UnboundLocalError kab trigger hota hai?** -> Jab function me kisi variable ko assign karne se pehle read kiya jaye (Python variable assignment dekh kar poore function scope me use local mark kar deta hai).
2. **Default Mutable Argument Trap kya hota hai?** -> `def append_to(item, target=[])`: Function definitions parse time par single default list create hoti hai jo subsequent calls me shared rehti hai (Fix: `target=None`).
3. **`globals()` vs `locals()` dictionaries me kya difference hai?** -> `globals()` actual module namespace dictionary ka direct reference return karta hai; `locals()` CPython me fast local variables array ka read-only copy snapshot return karta hai.

---
**Next Topic:** 06. Comprehensions & The Walrus Operator (:=) for High Performance

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1 Questions

Easy

1. State Tracking Closure with Nonlocal

Ek closure function `make_accumulator(initial=0)` likhein jo `nonlocal` ka use karke internal total track kare aur har call par added value accumulate kare.

                                        acc = make_accumulator(10); acc(5) -> 15; acc(20) -> 35                                    

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• Use `nonlocal total` inside the inner function.

Python 3.12

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🎯 Big Tech Coding & Interview Challenges

1. State Tracking Closure with Nonlocal

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Rishabh Gehlot

PHP 8+ & Laravel 11 Master Track