Scope and Lifetime - codenoteshub.com

► Understanding Scope and Lifetime

Scope and lifetime are fundamental concepts that determine where and how long variables exist in your program. Scope defines where a variable can be accessed, while lifetime determines how long a variable stays in memory.

► Real-World Analogy

Think of scope and lifetime like access to different rooms in a house:
» Your bedroom is your private space (local scope) – only you can access items there
» The living room is shared space (global scope) – everyone in the house can access it
» A note you write exists only while you’re in that room (lifetime)
» Once you leave and close the door, temporary notes disappear (variable destroyed)

► Key Concepts

✓ Local scope: Variables created inside functions
✓ Global scope: Variables created outside all functions
✓ Lifetime: Duration a variable exists in memory
✓ LEGB rule: Local, Enclosing, Global, Built-in lookup order
✓ Variable shadowing: Local variables can hide global ones

■ Code Examples

# Local scope example
def greet():
    message = "Hello"  # Local variable
    print(message)

greet()
# print(message)  # Error: message not accessible outside function

# Global scope example
count = 0  # Global variable

def increment():
    global count
    count += 1
    print(f"Count: {count}")

increment()
increment()
print(f"Final count: {count}")

# Variable shadowing
x = 10  # Global x

def show_x():
    x = 5  # Local x (shadows global)
    print(f"Local x: {x}")

show_x()
print(f"Global x: {x}")

# Local scope example

def greet():

message = "Hello" # Local variable

print(message)

greet()

# print(message) # Error: message not accessible outside function

# Global scope example

count = 0 # Global variable

def increment():

global count

count += 1

print(f"Count: {count}")

increment()

print(f"Final count: {count}")

# Variable shadowing

x = 10 # Global x

def show_x():

x = 5 # Local x (shadows global)

print(f"Local x: {x}")

show_x()

print(f"Global x: {x}")