How to Use Global Keyword in Python: Syntax and Examples

In Python, use the global keyword inside a function to modify a variable defined outside that function. This tells Python to use the global variable instead of creating a new local one.

Syntax

The global keyword is used inside a function to declare that a variable refers to the global scope variable. This allows you to modify the global variable from within the function.

• global variable_name: Declares the variable as global.
• After this declaration, assignments affect the global variable, not a local copy.

python

def function():
    global variable_name
    variable_name = new_value

Example

This example shows how to use global to change a variable defined outside the function.

python

count = 0

def increment():
    global count
    count += 1

print(f'Before increment: {count}')
increment()
print(f'After increment: {count}')

Output

Before increment: 0
After increment: 1

Common Pitfalls

Without global, assigning a value to a variable inside a function creates a new local variable, leaving the global variable unchanged. This often causes bugs when you expect the global variable to update.

Also, using global unnecessarily can make code harder to understand and debug.

python

x = 5

def wrong():
    x = 10  # This creates a local variable, does not change global x

wrong()
print(x)  # Output: 5

def right():
    global x
    x = 10  # This changes the global variable

right()
print(x)  # Output: 10

Output

5
10

Quick Reference

• Use global inside functions to modify global variables.
• Declare global before assigning to the variable.
• Without global, assignments create local variables.
• Use global sparingly to keep code clear.

Key Takeaways

Use global inside a function to modify a variable defined outside it.

Without global, assignments inside functions create local variables.

Declare global before assigning to the variable to affect the global scope.

Avoid overusing global to keep your code easy to understand.

Remember global only works inside functions, not in global scope.