Python Functions

A function is a block of code that performs a specific task.

Suppose we need to create a program to make a circle and color it. We can create two functions to solve this problem:

1. function to create a circle
2. function to color the shape

Dividing a complex problem into smaller chunks makes our program easy to understand and reuse.

Create a Function

Let's create our first function.

def greet():
    print('Hello World!')

Here are the different parts of the program:

Here, we have created a simple function named greet() that prints Hello World!

Calling a Function

In the above example, we have declared a function named greet().

def greet():
    print('Hello World!')

If we run the above code, we won't get an output.

It's because creating a function doesn't mean we are executing the code inside it. It means the code is there for us to use if we want to.

To use this function, we need to call the function.

Function Call

greet()

Example: Python Function Call

def greet():
    print('Hello World!')

# call the function
greet()

print('Outside function')

Output

Hello World!
Outside function

In the above example, we have created a function named greet(). Here's how the control of the program flows:

Here,

1. When the function greet() is called, the program's control transfers to the function definition.
2. All the code inside the function is executed.
3. The control of the program jumps to the next statement after the function call.

Python Function Arguments

Arguments are inputs given to the function.

def greet(name):
    print("Hello", name)

# pass argument
greet("John")

Sample Output 1

Hello John

Here, we passed 'John' as an argument to the greet() function.

We can pass different arguments in each call, making the function re-usable and dynamic.

Let's call the function with a different argument.

greet("David")

Sample Output 2

Hello David

Example: Function to Add Two Numbers

# function with two arguments
def add_numbers(num1, num2):
    sum = num1 + num2
    print("Sum: ", sum)

# function call with two values
add_numbers(5, 4)

Output

Sum: 9

In the above example, we have created a function named add_numbers() with arguments: num1 and num2.

def print_age(age):  # age is a parameter
    print(age)

print_age(25)  # 25 is an argument

The return Statement

We return a value from the function using the return statement.

# function definition
def find_square(num):
    result = num * num
    return result

# function call
square = find_square(3)

print('Square:', square)

Output

Square: 9

In the above example, we have created a function named find_square(). The function accepts a number and returns the square of the number.

Note: The return statement also denotes that the function has ended. Any code after return is not executed.

The pass Statement

The pass statement serves as a placeholder for future code, preventing errors from empty code blocks.

It's typically used where code is planned but has yet to be written.

def future_function():
    pass

# this will execute without any action or error
future_function()  

Note: To learn more, visit Python Pass Statement.

Python Library Functions

Python provides some built-in functions that can be directly used in our program.

We don't need to create the function, we just need to call them.

Some Python library functions are:

1. print() - prints the string inside the quotation marks
2. sqrt() - returns the square root of a number
3. pow() - returns the power of a number

These library functions are defined inside the module. And to use them, we must include the module inside our program.

For example, sqrt() is defined inside the math module.

Note: To learn more about library functions, please visit Python Library Functions.

Example: Python Library Function

import math

# sqrt computes the square root
square_root = math.sqrt(4)

print("Square Root of 4 is",square_root)

# pow() comptes the power
power = pow(2, 3)

print("2 to the power 3 is",power)

Output

Square Root of 4 is 2.0
2 to the power 3 is 8

Here, we imported a math module to use the library functions sqrt() and pow().

def greet(name, message="Hello"):
    print(message, name)

# calling function with both arguments
greet("Alice", "Good Morning")

# calling function with only one argument
greet("Bob")

Good Morning Alice
Hello Bob

# function to sum any number of arguments
def add_all(*numbers):
    return sum(numbers)

# pass any number of arguments
print(add_all(1, 2, 3, 4))   

10

# function to print keyword arguments
def greet(**words):
    for key, value in words.items():
        print(f"{key}: {value}")

# pass any number of keyword arguments
greet(name="John", greeting="Hello")

name: John
greeting: Hello

Also Read:

• Python Recursive Function
• Python Modules
• Python Generators