import { Callout } from '@/components/callout';

Creating Functions in Python

While Python has many built-in functions, its real power comes from allowing you to define your own. A function is a reusable block of code that performs a specific task. It only runs when it is called, can accept data (known as parameters), and can return data as a result.

Functions are the primary tool for organizing and structuring your code, making it more modular, readable, and maintainable. Functions you create work just like the built-in ones you've already used, such as print() or len().

Scripts vs. Functions

It's important to understand the difference between a simple script and a program built with functions.

• Scripts

  • A collection of commands executed sequentially, as if you typed them in the editor.
  • Primarily used for automating simple, repetitive tasks.
  • All variables exist in the same global workspace.

• Functions

  • Operate on specific inputs (parameters) and produce outputs (return values).
  • Have their own separate workspace; internal variables are local and don't interfere with the rest of the program.
  • Designed for reusability and abstraction.

Basic Function Syntax

In Python, a function is defined using the def keyword, followed by the function name, parentheses (), and a colon :. The code block within the function is indented. The return statement is used to send a value back from the function.

def function_name(parameter1, parameter2):
  # Code block to be executed
  statement_1
  statement_2
  return result

<Example title="A Simple add Function"> This function takes two numbers, x and y, as parameters and returns their sum.

# Define the function
def add(x, y):
  return x + y

# Call the function with arguments
x_val = 2
y_val = 5
z = add(x_val, y_val)

print(z) # Output: 7

</Example>

Organizing Code: Functions in Separate Files

For better organization, you can define your functions in one file and call them from another. A file containing function definitions is called a module.

<Example title="Creating and Importing a Custom Module"> Let's create a module with a function that calculates an average.

1. Create the module file (myfunctions.py): Save this code in a file named myfunctions.py. This function takes two numbers and returns their average.

# Filename: myfunctions.py

def average(x, y):
  return (x + y) / 2

2. Create the main script file (testaverage.py): In a separate file, you can import your average function from the myfunctions module and use it.

# Filename: testaverage.py

# Import the specific function from our module
from myfunctions import average

a = 2
b = 3

# Call the imported function
c = average(a, b)

print(c) # Output: 2.5

</Example>

Functions with Multiple Return Values

A Python function can return multiple values by separating them with a comma in the return statement. This is a powerful feature for bundling related results.

<Example title="Calculating Statistics"> This function takes a list of data and returns both the total sum and the mean.

# Define a function that returns two values
def calculate_stats(data_list):
  total_sum = 0
  for x in data_list:
    total_sum = total_sum + x
  
  n = len(data_list)
  mean = total_sum / n
  
  return total_sum, mean

# A list of data
data = [1, 5, 6, 3, 12, 3]

# Call the function and unpack the returned values into two variables
sum_val, mean_val = calculate_stats(data)

print(f"Sum: {sum_val}, Mean: {mean_val}")
# Output: Sum: 30, Mean: 5.0

</Example>

Exercises

The best way to learn is by doing. Try solving the following problems.

<Exercise title="Calculate Average Function"> Create a function named calc_average that takes two numbers as input and returns their average. Test it to make sure it works. </Exercise>

<Exercise title="Angle Conversion Functions"> Most trigonometric functions in Python's math module work with radians. Create your own module with two functions:

• degrees_to_radians(d): Converts an angle from degrees to radians.
• radians_to_degrees(r): Converts an angle from radians to degrees.

The conversion formulas are:

• $r[\text{radians}] = d[\text{degrees}] \times (\frac{\pi}{180})$
• $d[\text{degrees}] = r[\text{radians}] \times (\frac{180}{\pi})$

Test both functions to ensure they work correctly. (Hint: math.pi provides the value of $\pi$). </Exercise>

<Exercise title="Fibonacci Function"> Create a function that implements the Fibonacci sequence. The function should take an integer N as a parameter and return a list containing the first N Fibonacci numbers. The sequence begins 0, 1, 1, 2, 3, 5, ..., where each subsequent number is the sum of the previous two. </Exercise>

<Exercise title="Prime Number Checker"> A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. Create a function is_prime(number) that takes an integer as input and returns True if the number is prime, and False otherwise. (Hint: You may need to use nested loops). </Exercise>