05 Functions

Funtions in Python #

Introduction #

Functions are reusable blocks of code that perform a specific task. They implement na algorithm. Moreover, they help us organize and structure our programs, avoid repetition, and improve readability.

Function reduce complexity, as the user (caller) of a function doesn’t need to know the algorithm, only what’s the input and expected output. Thus, from the perspective of the caller of the function it is a blackbox.

Functions are one of the most importants concepts in programming.

A function in Python is defined using the def keyword:

# Defining function
def greet():
    print("Hello, World!")

# Calling the function
greet()

A function like greet that doesn’t contain a return statement automatically returns the value None. As such it is also called a procedure. A proper function returns a value. Example:

def calculate_circumference(radius):
    if radius < 0:
        raise ValueError("Radius cannot be negative")
    pi = 3.141592653589793
    return 2 * pi * radius

radius = 5
circumference = calculate_circumference(radius)
print(f"The circumference of a circle with radius {radius} is {circumference}")

When a return statement is executed, the function terminates at that point returning the value to the caller and gives control to the caller.

Arguments #

Functions can accept inputs called arguments. These allow the function to work with dynamic data.

Positional Arguments #

Positional arguments are the most common type. Their order is important:

def greet_person(name):   # `name` is a positional argument
    print(f"Hello, {name}!")

greet_person("Alice")

The values passed to a function in the place of an argument are called parameters. So in the example above the parameter for greet_person is "Alice".

Default Arguments #

Default arguments have predefined values. If not provided during the call, the default is used:

def greet_person(name="Stranger"):
    print(f"Hello, {name}!")

# Calling the function
greet_person()       # Uses default value
greet_person("Bob")  # Overrides default value

Variable Argument List #

Sometimes, you may not know how many arguments will be passed to the function. You can use *args to accept a variable number of arguments:

def greet_people(*names):
    for name in names:
        print(f"Hello, {name}!")

greet_people("Alice", "Bob", "Charlie")

Keyword Arguments #

def describe_person(**details):
    for key, value in details.items():
        print(f"{key}: {value}")

# Calling the function
describe_person(name="Alice", age=25, location="New York")

Docstrings #

A docstring is a special string that describes what the function does. It is written as the first statement inside the function body and is usually enclosed in triple quotes (""" or ‘’’).

# Example: Function with Docstring
def greet_person(name):
    """
    Greets a person with the provided name.

    Args:
        name (str): The name of the person to greet.

    Returns:
        None
    """
    print(f"Hello, {name}!")

print(greet_person.__doc__)   # Accessing a function's docstring
greet_person('Peter')         # Calling is as usual

Homework (graded) #

Basic Function #

Write a function say_hello that prints “Hello, Python!”. Call the function to ensure it works.

Positional and Default Arguments #

Write a function introduce that takes two arguments: name and age (default value for age should be 18). Print a sentence introducing the person. Call the function with both arguments and with only name.

Variable Arguments #

Write a function list_hobbies that accepts any number of hobby names using *args. Print all hobbies passed to the function. Call the function with at least three hobby names.

Keyword Arguments #

Write a function person_details that accepts name, age, and city as keyword arguments. Print these details in a formatted string. Call the function using keyword arguments in different orders.

Arbitrary Keyword Arguments #

Write a function profile that accepts any number of keyword arguments using **kwargs. Print all the key-value pairs in a readable format. Call the function with at least three key-value pairs.

Docstring #

Write a function calculate_area that calculates and returns the area of a rectangle given length and width. Add a docstring explaining the purpose of the function, its arguments, and what it returns. Access and print the docstring. Call the function to test it.

Combo #

Combine all these concepts into a single function full_profile that takes:

  • A mandatory positional argument for name.
  • A default argument for age.
  • An arbitrary list of hobbies using *args.
  • Additional details using **kwargs.

Print the complete profile in a structured format.

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