Python Functions

Functions are a block of code that performs a specific task. They allow us to split our program into reusable parts.

We can define a function in Python using the def keyword. A basic function definition has the following components:

def: Indicates that a function is being defined
function_name(): The name of the function
Parameters (optional): The parameters passed to the function enclosed in parentheses ()
colon :
Indented Block: The code block with the statements to be executed.

For example:

def add(x, y):
    return x + y

Here:

def indicates we are defining a function
add() is the function name
(x, y) are the parameters
The indented block contains the return statement to return the sum of x and y

We can call the function like this:

result = add(2,3)
print(result)
# Prints 5

Scope

In Python, variables can have either global or local scope.

Global scope:

Variables declared outside of a function are known as global variables and have global scope.
They can be accessed inside and outside of functions.

Local scope:

Variables declared inside a function are local to that function.
They can only be accessed within that function.

For example:

x = "global" # global

def func():
    y = "local" # local

    print(x) # Can access global x
    print(y) # Can only access local y

func()
print(x) # Can access global x
# print(y) # Will give an error as y is local to func()

Output:

global  
local
global

To use a global variable inside a function, we need to declare it as global. For example:

x = "global"

def func():
    global x   # Declaring x as global
    x = "local"

    print(x)

func()
print(x)

Output:

local  
local

So in summary, global variables can be accessed inside and outside functions while local variables are only accessible within the function in which they are declared.

Global & Nonlocal

The global and nonlocal keywords in Python are used to modify variables outside of the current scope.

global - It is used to modify a variable from the global scope within a function.

For example:

x = "global"

def func():
    global x  
    x = "modified"

func()

print(x) # prints modified

Here we use global x to modify the global variable x from within the function.

nonlocal - It is used to modify a variable from an enclosing scope within a nested function.

For example:

def outer():
    x = "outer"

    def inner():
        nonlocal x
        x = "inner"

    inner()
    print(x) # prints inner

outer()

Here we use nonlocal x to modify the variable x from the enclosing outer() scope within the inner() function.

Without nonlocal, inner() would create a new local variable x and modify that, leaving the outer x unchanged.

So in summary:

global modifies a variable from the global scope
nonlocal modifies a variable from an enclosing scope (not the global scope)

Both allow us to modify variables outside of the current local scope from within a function.

Shadowing

Shadowing refers to a situation where a local variable shares the same name as a global variable, hiding or shadowing the global variable.

For example:

x = "global"

def func():
    x = "local"
    print(x) # Prints local

func()  
print(x) # Prints global

Here, the local x inside func() shadows the global x, hiding it. The local x takes precedence and is printed.

After func() returns, the global x is accessible again and is printed.

So in summary:

When a local variable shares the same name as a global variable, the local variable shadows the global one.
Within the scope of the local variable, the global variable is hidden.
After the local scope ends, the global variable is accessible again.

This is known as the shadowing effect.

We can avoid shadowing by:

Using different variable names
Using the global keyword to modify the global variable from within the local scope.

For example:

x = "global"

def func():
    global x
    x = "local"
    print(x) # Prints local

func()  
print(x) # Also prints local

Here we use global x to modify the global x from within the local scope, avoiding shadowing.

Disclaim: This article is created with Rix AI. I ask the questions so you don't have to. Learn and prosper. 🖖

Python Functions

Introduction to python functions and subprograms

Table of contents

Scope

Global & Nonlocal

Shadowing