Python Basics — Day 17 Local vs Global Variables & Scope

01. Local Variables

• Declared inside a function

• Exist only while the function is running

def show_number():
    x = 10   # Local variable
    print("Inside function:", x)

show_number()
# print(x)   # Error! (x is not defined outside the function)

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02. Global Variables

• Declared outside of any function

• Can be accessed anywhere in the program

y = 20   # Global variable

def print_global():
    print("Inside function:", y)

print_global()
print("Outside function:", y)

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03. Modifying a Global Variable with global

count = 0

def increase():
    global count   # Declare to use the global variable
    count += 1

increase()
increase()
print(count)   # 2

⚠️ Note: Avoid overusing global, as it can make code harder to manage.

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04. Name Conflict Between Local and Global Variables

x = 100

def test():
    x = 50   # Local variable (different from global x)
    print("Inside function:", x)

test()
print("Outside function:", x)
# Inside function: 50
# Outside function: 100

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05. Scope Rules (LEGB Rule)

Python searches for variables in the following order:

• L (Local) – Inside the current function

• E (Enclosed) – In the enclosing (outer) function

• G (Global) – In the global scope

• B (Built-in) – In Python’s built-in namespace

x = "global"

def outer():
    x = "enclosed"
    def inner():
        x = "local"
        print(x)   # local
    inner()
    print(x)       # enclosed

outer()
print(x)           # global

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06. The nonlocal Keyword

• Used inside nested functions to modify a variable in the enclosing function

def outer():
    x = "enclosed"
    def inner():
        nonlocal x
        x = "changed"
        print("inner:", x)
    inner()
    print("outer:", x)

outer()

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07. Practice Examples

Example 1: Local vs Global

a = 5

def func():
    a = 10
    print("Inside function:", a)

func()
print("Outside function:", a)

Example 2: Using global

counter = 0

def add():
    global counter
    counter += 1

add()
add()
print(counter)   # 2

Example 3: Using nonlocal

def outer():
    msg = "Hello"
    def inner():
        nonlocal msg
        msg = "Hi"
    inner()
    print(msg)

outer()