Python Functions Explained Simply

Write reusable code blocks that make your programs cleaner and more powerful

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By Prakash Gangurde | BCA Student | Technical Content Creator | AI • Python • Linux

Part 2 of the Python for Absolute Beginners series

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Introduction

Imagine you are writing a program that calculates a student's grade. You write the logic once. Then you realize you need to calculate the grade again in another part of the program. Do you copy and paste the same code?

No — you use a function.

A function is a block of code you write once and can use as many times as you need. It is one of the most important concepts in programming, and once you understand it, your code will become cleaner, shorter, and far easier to read.

In this article you will learn:

• What a function is and why it matters

• How to define and call a function in Python

• The difference between parameters and arguments

• How return values work

• How to use default parameters

• How to build a real project using everything you learn

Estimated reading time: 12–15 minutes This is Part 2 of the Python for Absolute Beginners series. If you have not read Part 1, start here: Python Basics for Absolute Beginners

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What Is a Function?

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

Think of it like a coffee machine. You press one button and it does everything — grinds the beans, heats the water, and pours the coffee. You do not need to know how it works internally. You just press the button and get the result.

In Python, a function works the same way:

• You define it once (build the coffee machine)

• You call it whenever you need it (press the button)

Without functions, your code looks like this — repetitive and hard to manage:

# Without functions — repeated code
student1_score = 85
if student1_score >= 90:
    print("Grade: A")
elif student1_score >= 75:
    print("Grade: B")
elif student1_score >= 60:
    print("Grade: C")
else:
    print("Grade: F")

student2_score = 72
if student2_score >= 90:
    print("Grade: A")
elif student2_score >= 75:
    print("Grade: B")
elif student2_score >= 60:
    print("Grade: C")
else:
    print("Grade: F")

With functions, the same logic becomes:

# With functions — clean and reusable
def get_grade(score):
    if score >= 90:
        return "A"
    elif score >= 75:
        return "B"
    elif score >= 60:
        return "C"
    else:
        return "F"

print(get_grade(85))   # B
print(get_grade(72))   # C
print(get_grade(95))   # A

Same result. Half the code. Much easier to fix if something goes wrong.

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Defining a Function — The def Keyword

To create a function in Python, you use the def keyword.

Here is the basic structure:

def function_name():
    # code goes here

Let's write the simplest possible function:

def greet():
    print("Hello! Welcome to Python.")

To run (call) the function, you write its name followed by parentheses:

greet()

Output:

Hello! Welcome to Python.

You can call it as many times as you want:

greet()
greet()
greet()

Output:

Hello! Welcome to Python.
Hello! Welcome to Python.
Hello! Welcome to Python.

The code inside greet() runs every time you call it — without you having to rewrite it.

Important: Indentation

Python uses indentation (spaces at the start of a line) to know what belongs inside a function. Every line inside the function must be indented by 4 spaces or one Tab.

def greet():
    print("This is inside the function")   # ✅ indented — belongs to greet()

print("This is outside the function")     # ✅ no indent — runs separately

If you forget the indent, Python throws an IndentationError:

def greet():
print("Hello")   # ❌ IndentationError — not indented

This is one of the most common mistakes for beginners. Always indent your function body.

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Parameters and Arguments

Right now our greet() function always prints the same message. What if we want to greet different people by name?

This is where parameters come in.

A parameter is a variable you define inside the function parentheses — it acts as a placeholder for the value that will be passed in.

def greet(name):       # name is a parameter
    print(f"Hello, {name}! Welcome to Python.")

When you call the function, you pass the actual value — this is called an argument:

greet("Prakash")       # "Prakash" is the argument
greet("Rahul")
greet("Priya")

Output:

Hello, Prakash! Welcome to Python.
Hello, Rahul! Welcome to Python.
Hello, Priya! Welcome to Python.

The difference between parameters and arguments

This confuses many beginners because tutorials use these words interchangeably. They are not the same:

def greet(name):        # name = PARAMETER (the placeholder in the definition)
    print(f"Hello, {name}!")

greet("Prakash")        # "Prakash" = ARGUMENT (the actual value you pass)

Simple way to remember:

• Parameter = the placeholder when you define the function

• Argument = the actual value when you call the function

Multiple parameters

A function can take more than one parameter:

def introduce(name, age, course):
    print(f"My name is {name}. I am {age} years old and studying {course}.")

introduce("Prakash", 21, "BCA")
introduce("Rahul", 20, "BSc CS")

Output:

My name is Prakash. I am 21 years old and studying BCA.
My name is Rahul. I am 20 years old and studying BSc CS.

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Return Values

So far our functions print things to the screen. But what if you want a function to give you back a value that you can use later?

That is what the return keyword does.

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

When you call this function, it gives back the result:

result = add(10, 5)
print(result)          # 15

You can use the returned value directly in calculations:

total = add(10, 5) + add(3, 7)
print(total)           # 25

print vs return — understanding the difference

This trips up almost every beginner:

# Using print inside function
def add_print(a, b):
    print(a + b)       # displays the result but gives nothing back

# Using return inside function
def add_return(a, b):
    return a + b       # gives the result back to use later

# The difference:
add_print(3, 4)        # prints 7, but you can't store it
result = add_return(3, 4)   # stores 7 in result — you can use it
print(result * 2)      # 14

Rule of thumb:

• Use print when you just want to display something

• Use return when you want to use the result later in your program

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Default Parameters

Sometimes you want a function to have a default value if no argument is passed.

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

Now you can call it two ways:

greet("Prakash")              # uses default greeting
greet("Rahul", "Good morning")  # uses custom greeting

Output:

Hello, Prakash!
Good morning, Rahul!

Default parameters must always come after regular parameters. This will cause an error:

def greet(greeting="Hello", name):   # ❌ SyntaxError
    print(f"{greeting}, {name}!")

This is correct:

def greet(name, greeting="Hello"):   # ✅ default parameter at the end
    print(f"{greeting}, {name}!")

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A Note About input() and Types

Before we build our project, one important thing to remember from Part 1:

input() always returns a string — even if the user types a number.

age = input("Enter your age: ")
print(type(age))     # <class 'str'>  — it's text, not a number

If you want to use it as a number, convert it:

age = int(input("Enter your age: "))    # converts to integer
score = float(input("Enter score: "))   # converts to decimal number

This matters in our project below because we will be working with scores.

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Real Project — Student Report Card Generator

Let us build something genuinely useful. This program uses multiple functions to generate a complete student report card.

# Student Report Card Generator
# Written by Prakash Gangurde

def get_grade(score):
    """Returns the letter grade for a given score."""
    if score >= 90:
        return "A"
    elif score >= 75:
        return "B"
    elif score >= 60:
        return "C"
    elif score >= 40:
        return "D"
    else:
        return "F"

def calculate_percentage(total, max_marks):
    """Calculates percentage from total marks obtained."""
    return round((total / max_marks) * 100, 2)

def get_remarks(percentage):
    """Returns remarks based on percentage."""
    if percentage >= 90:
        return "Outstanding"
    elif percentage >= 75:
        return "Excellent"
    elif percentage >= 60:
        return "Good"
    elif percentage >= 40:
        return "Needs Improvement"
    else:
        return "Please seek academic support"

def print_report(name, scores):
    """Prints a formatted report card for the student."""
    subjects = ["Python", "Linux", "Web Dev", "Cybersecurity", "Database"]
    total = sum(scores)
    max_marks = len(subjects) * 100
    percentage = calculate_percentage(total, max_marks)
    remarks = get_remarks(percentage)

    print()
    print("=" * 40)
    print("       STUDENT REPORT CARD")
    print("=" * 40)
    print(f"Name       : {name}")
    print("-" * 40)

    for subject, score in zip(subjects, scores):
        grade = get_grade(score)
        print(f"{subject:<15} {score}/100     Grade: {grade}")

    print("-" * 40)
    print(f"Total      : {total}/{max_marks}")
    print(f"Percentage : {percentage}%")
    print(f"Remarks    : {remarks}")
    print("=" * 40)

# --- Main Program ---
print("=== Student Report Card Generator ===")
print()

name = input("Enter student name: ")

print(f"\nEnter marks out of 100 for {name}:")
scores = []

subjects = ["Python", "Linux", "Web Dev", "Cybersecurity", "Database"]
for subject in subjects:
    score = int(input(f"  {subject}: "))
    scores.append(score)

print_report(name, scores)

Sample output:

=== Student Report Card Generator ===

Enter student name: Prakash Gangurde

Enter marks out of 100 for Prakash Gangurde:
  Python: 88
  Linux: 92
  Web Dev: 79
  Cybersecurity: 95
  Database: 83

========================================
       STUDENT REPORT CARD
========================================
Name       : Prakash Gangurde
----------------------------------------
Python          88/100     Grade: B
Linux           92/100     Grade: A
Web Dev         79/100     Grade: B
Cybersecurity   95/100     Grade: A
Database        83/100     Grade: B
----------------------------------------
Total      : 437/500
Percentage : 87.4%
Remarks    : Excellent
========================================

Notice what this project uses:

• 4 separate functions — each does one specific job

• Parameters and return values

• A loop to collect input

• zip() to pair subjects with scores

• sum() to total the scores

• f-strings for clean formatting

Each function is small, focused, and reusable. This is exactly how real programs are written.

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Try It Yourself — Challenge

Before moving to the next article, try this challenge:

Write a function called bmi_calculator that takes two parameters: weight (in kg) and height (in metres). It should return the BMI value using the formula: BMI = weight / (height × height) Then write another function called bmi_category that takes the BMI value and returns:

• "Underweight" if BMI < 18.5

• "Normal" if BMI is 18.5–24.9

• "Overweight" if BMI is 25–29.9

• "Obese" if BMI >= 30

This uses everything from this article: functions, parameters, return values, and conditions.

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What to Learn Next

You now understand functions — one of the most important building blocks in programming. Here is what comes next:

Topic	What it does
Lists and Tuples	Store collections of data
Loops	Repeat actions automatically
Dictionaries	Store key-value pairs
File Handling	Read and write files
Modules	Import and use existing code

Each of these will be covered in the next articles in this series.

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Summary — What You Learned Today

• ✅ What a function is and why it makes code better

• ✅ How to define a function using the def keyword

• ✅ The difference between parameters and arguments

• ✅ How return gives back values from a function

• ✅ How default parameters work

• ✅ Why indentation matters inside functions

• ✅ How to build a real project using multiple functions together

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All Code on GitHub

Every code example from this article is in my GitHub repository:

📌 GitHub: github.com/prakashgangurde-ux/python-basics

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Let's Connect

If this article helped you, please clap on Medium — it helps other beginners find it.

Drop any question in the comments — I read and reply to every one.

• LinkedIn: linkedin.com/in/prakashgangurde

• GitHub: github.com/prakashgangurde-ux

• Medium: medium.com/@gangurdeprakash

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Next article: Lists in Python — Store and Manage Collections of Data

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Written by Prakash Gangurde — BCA Student | Technical Content Creator | AI • Python • Linux