Python Basics - 11. Scope, Closures, and Decorators

This notebook explains variable scope (LEGB), closures, and decorators. These topics are key to understanding how Python functions behave in real projects.

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1. LEGB Scope Rule

Python resolves names in this order: Local, Enclosing, Global, Built-in.

message = "global"

def outer():
    message = "enclosing"
    def inner():
        message = "local"
        print(f"Inner sees: {message}")
    inner()
    print(f"Outer sees: {message}")

outer()
print(f"Global sees: {message}")

Inner sees: local
Outer sees: enclosing
Global sees: global

2. Closures

A closure is an inner function that remembers values from its enclosing scope even after the outer function returns.

def make_multiplier(factor):
    def multiply(x):
        return x * factor
    return multiply

double = make_multiplier(2)
triple = make_multiplier(3)
print(double(10), triple(10))

20 30

3. Decorators

A decorator wraps a function to add behavior before/after execution without changing the original function body.

def log_call(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__} with args={args}, kwargs={kwargs}")
        result = func(*args, **kwargs)
        print(f"{func.__name__} returned {result}")
        return result
    return wrapper

@log_call
def add(a, b):
    return a + b

add(5, 7)

Calling add with args=(5, 7), kwargs={}
add returned 12

12