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⭐ Scope and Lifetime of Variables in Python

In Python, scope and lifetime determine:

✔ Where a variable can be accessed
✔ How long a variable exists in memory

These concepts are very important in functions and control structures.

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1. Scope of a Variable

Scope = the region of the program where a variable is accessible (visible).

Python follows the LEGB Rule for scope:

⭐ L – Local

⭐ E – Enclosing (Nonlocal)

⭐ G – Global

⭐ B – Built-in

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⭐ A. Local Scope (Inside Function)

A variable defined inside a function.

def func():
    x = 10   # local variable
    print(x)

func()
print(x)     # ❌ Error: x not accessible outside function

✔ Exists only inside function
✔ Not accessible outside

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⭐ B. Global Scope (Outside Function)

A variable defined outside all functions.

x = 20   # global variable

def func():
    print(x)  # accessible inside function

func()

✔ Accessible throughout program
✔ Accessible inside functions (read only)

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⭐ C. Enclosing Scope (Nonlocal)

Variables in inner function can access variables of outer function.

def outer():
    x = 10    # enclosing variable
    def inner():
        print(x)
    inner()

outer()

If you want to modify enclosing variable, use nonlocal.

def outer():
    x = 10
    def inner():
        nonlocal x
        x = 20
    inner()
    print(x)   # 20

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⭐ D. Built-in Scope

Functions and variables built into Python:

Examples:

• len()
• sum()
• range()
• print()

Available everywhere.

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2. Lifetime of a Variable

Lifetime = duration for which a variable exists in memory.

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⭐ A. Lifetime of Local Variables

Local variables:

✔ Created when function is called
✔ Destroyed when function finishes

def func():
    x = 10
    print(x)

func()  
print(x)   # ❌ not available

Lifetime ends after function execution.

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⭐ B. Lifetime of Global Variables

Global variables:

✔ Created when program starts
✔ Destroyed when program ends

x = 50

def show():
    print(x)

show()

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⭐ C. Lifetime of Enclosing Variables

Enclosing scope variables exist as long as the outer function exists.

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3. Using global Keyword

If you want to modify a global variable inside a function, use global.

x = 10

def update():
    global x
    x = 20

update()
print(x)   # 20

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4. Using nonlocal Keyword

Used to modify an enclosing function variable inside inner function.

def outer():
    x = 5
    def inner():
        nonlocal x
        x = 15
    inner()
    print(x)

outer()

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⭐ 5. LEGB Rule Summary

Level	Description
L – Local	Inside the current function
E – Enclosing	Inside outer functions
G – Global	Top-level of module
B – Built-in	Python’s built-in scope

Python searches variables in this order:
Local → Enclosing → Global → Built-in

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⭐ Exam-Ready Summary

✔ Scope defines where a variable is accessible
✔ Lifetime defines how long a variable exists in memory

Local Variable

• Declared inside function
• Exists till function ends

Global Variable

• Declared outside functions
• Exists till program ends

Enclosing Variable

• Defined in outer function
• Accessible to inner function

global keyword

Used to modify global variables

nonlocal keyword

Used to modify enclosing variables

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