Understanding Functions In Python

In this Python tutorial, we will discuss, what is a function in Python, Python function syntax, and how to define a function in Python. Also, I will show you how to call a function in Python.

Table of Contents

What is a Function in Python?

In Python, a function is a reusable block of code that performs a specific task. Functions allow you to break down your program into smaller, modular chunks. This results in cleaner, more readable code that is easier to maintain and debug.

Syntax of a Function in Python

To define a function in Python, you use the def keyword, followed by the function name, parentheses, and a colon. The code block within a function is indented.

def function_name(parameters):
    # code
    return # optional return statement

def: Keyword that informs Python that you’re defining a function.
function_name: The name you assign to your function.
parameters: Optional. Values you can pass into the function.
return: Optional. Use this statement to pass a value back from the function.

How to Define a Function in Python

Let’s create a simple function named greet that prints a greeting message:

def greet(name):
    print(f"Hello, {name}!")

Here, greet is the function name, and name is the parameter it accepts.

How to Call a Function in Python

After defining a function, you can call it by using its name followed by parentheses. You can pass values (arguments) inside these parentheses if the function expects parameters.

READ: Endswith function in Python string

Let us see, how we can call the above function.

greet("Alice")  # This will output "Hello, Alice!"

Return Statement

A function can return a value using the return statement. Once a return statement is executed, the function terminates and passes the specified value back to the caller.

Example:

def add(a, b):
    sum = a + b
    return sum

result = add(2, 3)  # result will be 5
print(result)

Real Example of a Python Function

Let us check a complete example of how to define and call a function in Python.

In this example, let’s define a function called greet_names that accepts a list of names and returns a list of personalized greeting messages.

def greet_names(names):
    """
    Create greeting messages for a list of names.

    :param names: A list of names.
    :return: A list of personalized greeting messages.
    """

    # List to store the greeting messages
    greetings = []

    # Loop through each name in the names list
    for name in names:
        # Create a personalized greeting message
        greeting = f"Hello, {name}! Welcome to the USA!"
        
        # Append the greeting message to the greetings list
        greetings.append(greeting)

    # Return the list of greeting messages
    return greetings

Now, let’s call this function with a list of names and print the personalized greeting messages.

# Define a list of names
names = ["Alice", "Bob", "Charlie", "Diana"]

# Call the function and store the returned greeting messages
greeting_messages = greet_names(names)

# Print each greeting message
for message in greeting_messages:
    print(message)

Now, when you run the above code, you can see the output like in the below screenshot.

Common Built-in Functions

Python provides a host of built-in functions. Here’s a table with some of the commonly used ones:

Function	Description
`len(s)`	Returns the length of an object `s`.
`max(iterable)`	Returns the largest item in an iterable.
`min(iterable)`	Returns the smallest item in an iterable.
`sum(iterable)`	Returns the sum of all items in an iterable.
`type(obj)`	Returns the type of an object `obj`.
`sorted(iterable)`	Returns a sorted list of the specified iterable.
`round(number, ndigits)`	Rounds a number to a specified number of decimals.
`print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)`	Prints the specified message to the screen.
`input(prompt)`	Allows user input.

Conclusion

In this Python tutorial, I have explained, how to define a function in Python, and how to call a function in Python. Also, we saw a few examples of built-in Python functions.

READ: Naming Convention in Python [With Examples]