Python Global Keyword

1. Basic Use of Global Variable

count = 10

def display():
    print(count)

display()  # Output: 10

Global variables are declared outside functions and are readable within functions by default.

---

2. Modifying Global Variable Without global (Error Case)

value = 5

def update():
    value = value + 1  # UnboundLocalError

Assigning to a variable inside a function makes it local unless explicitly declared global.

---

3. Using global to Modify Global Variable

counter = 0

def increment():
    global counter
    counter += 1

increment()
print(counter)  # Output: 1

The global keyword allows direct modification of a global variable.

---

4. Global Variable Across Multiple Functions

status = "inactive"

def activate():
    global status
    status = "active"

def show_status():
    print(status)

activate()
show_status()  # Output: active

A global variable can be shared and updated across multiple functions.

---

5. Global Keyword Inside Nested Functions

x = 100

def outer():
    def inner():
        global x
        x = 200

    inner()

outer()
print(x)  # Output: 200

global always refers to the module-level scope, even when used inside nested functions.

---

6. Difference Between global and nonlocal

x = 50

def outer():
    x = 10
    
    def inner():
        global x
        x = 99

    inner()
    print("Outer x:", x)

outer()
print("Global x:", x)

• global → Refers to module-level variable

• nonlocal → Refers to nearest enclosing function scope

---

7. Tracking State Using Global Variable

requests = 0

def handle_request():
    global requests
    requests += 1

handle_request()
handle_request()
print(requests)  # Output: 2

Used for maintaining application-wide counters or shared state.

---

8. Global Variable with Conditional Logic

mode = "light"

def toggle_mode():
    global mode
    if mode == "light":
        mode = "dark"
    else:
        mode = "light"

toggle_mode()
print(mode)  # Output: dark

Global variables often manage configuration state.

---

9. Avoiding Global Abuse (Best Practice Warning)

config = {"theme": "dark"}

def update_config(new_theme):
    config["theme"] = new_theme  # No global keyword needed

Mutable objects can be modified without global, reducing global keyword dependency.

---

10. Best Practice: Encapsulation Instead of Global

class Counter:
    def __init__(self):
        self.value = 0

    def increment(self):
        self.value += 1

counter = Counter()
counter.increment()
print(counter.value)  # Output: 1

Encapsulation is preferred over global variables in production systems for maintainability and testability.

---