5.6 Variable Scope

Understanding the scope of variables and the LEGB rule (Local, Enclosing, Global, Built-in) to avoid errors and manage data correctly.

The scope of a variable determines the part of the program from which that variable is accessible. Python follows the LEGB rule to find a variable:

Local (L): The innermost level, inside a function. Variables defined here are local.
Enclosing (E): The scope of outer functions, in case of nested functions.
Global (G): The top-level of a Python file. Variables defined here are global.
Built-in (B): The scope that contains Python's built-in functions (e.g., `print()`, `len()`).

Python searches for a variable in this order: L -> E -> G -> B. If it doesn't find it, it raises a `NameError`.

global and nonlocal Keywords

Normally, you cannot modify a global variable from a local scope. To do this, you must use the `global` keyword. Similarly, the `nonlocal` keyword is used within a nested function to modify a variable of the immediately enclosing function.

# Global Example
counter = 0

def increment_counter():
    global counter
    counter += 1

increment_counter()
increment_counter()
print(f"Global counter: {counter}")

# Nonlocal Example
def outer_function():
    message = "Outer"
    def inner_function():
        nonlocal message
        message = "Changed!"
    inner_function()
    print(f"Final message: {message}")

outer_function()

Practical Exercises

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5.6 Variable Scope

global and nonlocal Keywords

Practical Exercises

Exercise 1:Write a function calculate_rectangle_area that takes length and width and returns the area. Call it and print the result.

Exercise 2:Write a function create_email with parameters username and domain, and an optional parameter tld with a default value of "com". The function should return the full email.

Exercise 3:Write a function calculate_average that uses *args to accept a variable number of numbers and returns their average.

Exercise 4:Create a list of numbers. Use filter() with a lambda function to get only the numbers that are greater than 5 and less than 10.

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