Python Coding Day 13 | Functions, Loops, and Control Flow

Functions, Loops, and Control Flow

Watch the lesson tutorial  ðŸ”»


1. Python Functions: Building Reusable Code Blocks

A function is a self-contained block of organized, reusable code that performs a single, related action. Functions are defined using the def keyword and are essential for giving your code modularity and preventing repetition.

1.1 Defining and Calling a Function

  • The function definition starts with the def keyword.

  • It is followed by the function name and parentheses (), which may contain input parameters.

  • The code block inside the function must be indented.

Example Code:

Python
def greet_user(name):
    """This function greets the person passed in as a parameter."""
    print(f"Hello, {name}!")

# Calling the function to execute the code inside it
greet_user("Alice")
greet_user("Bob")

Output:

Hello, Alice!
Hello, Bob!

1.2 The Importance of Indentation

Indentation (usually 4 spaces) defines the function's scope—which lines of code belong to the function.

Example A: Code within the function (Indented)

Python
def print_greetings():
    print("hello") 
    print("world") # Both lines are indented and belong to the function

# Calling the function
print_greetings()

Output:

hello
world

Example B: Code outside the function (Not Indented)

Python
def print_hello():
    print("hello") # Indented, part of the function

print("world") # NOT indented, executes immediately when read

# Calling the function
print_hello()

Output (The un-indented line runs first):

world
hello

1.3 Returning Values from Functions

The return keyword is used to send a value back from the function to the point where it was called. This allows functions to calculate results and pass them to other parts of the program.

Example Code (Returning a single value):

Python
def add_numbers(a, b):
    """Calculates and returns the sum of two numbers."""
    result = a + b
    return result # Returns the value of 'result'

# Store the returned value in the variable 'sum1'
sum1 = add_numbers(10, 5)

print(f"The calculated sum is: {sum1}")

Output:

The calculated sum is: 15

Example Code (Returning multiple values):

Python
def calculate_rectangle_stats(length, width):
    area = length * width
    perimeter = 2 * (length + width)
    return area, perimeter # Returns a tuple (area, perimeter)

# Unpack the returned tuple
rect_area, rect_perimeter = calculate_rectangle_stats(8, 4)

print(f"Area: {rect_area}, Perimeter: {rect_perimeter}")

Output:

Area: 32, Perimeter: 24

2. Looping in Python: while and for

Loops allow a block of code to be executed repeatedly. Python provides two primary types of loops: while and for.

2.1 The while Loop (Condition-Based Repetition)

A while loop executes its body of code as long as a specified condition remains True. You must ensure that the condition eventually becomes False to avoid an infinite loop.

Example A: Infinite Loop (Condition never changes)

Python
x = 6
while x > 0:
    print("won")
    # x is never changed, so x > 0 is always True

Output:

won
won
won
... (repeats indefinitely)

Example B: Practical Finite Loop (Counting down)

Python
countdown_timer = 5

print("Starting countdown:")
while countdown_timer > 0:
    print(countdown_timer)
    # Crucial step: decrease the counter to eventually end the loop
    countdown_timer = countdown_timer - 1 

print("Lift off!")

Output:

Starting countdown:
5
4
3
2
1
Lift off!

2.2 The for Loop (Iteration Over Sequences)

A for loop is used to iterate over the items of any sequence (like a list or string) or other iterable objects.

Example A: Iterating Over a List

Python
fruits = ["apple", "banana", "cherry", "date"]

print("Available fruits:")
# The variable 'fruit' takes the value of each item in 'fruits'
for fruit in fruits:
    print(f"- {fruit}")

Output:

Available fruits:
- apple
- banana
- cherry
- date

Example B: Using range() for Fixed Repetitions

The range() function generates a sequence of numbers, perfect for running a loop a specific number of times.

Python
# range(5) generates numbers 0, 1, 2, 3, 4
for i in range(5):
    print(f"Loop count: {i}")

print("---")

# range(10, 13) generates numbers 10, 11, 12
for num in range(10, 13):
    print(num)

Output:

Loop count: 0
Loop count: 1
Loop count: 2
Loop count: 3
Loop count: 4
---
10
11
12


Run Today's Lesson Codes on Colabs (Click Here)

- by Chirana Nimnaka

Comments

Post a Comment

Popular posts from this blog

Python Coding Day 1 | The print() Function and Comments

Image
  Mastering Python Basics: The  print()  Function and Comments  Watch the lesson tutorial   🔻 The Python print() function is often the very first tool any developer learns, as it provides instant feedback and is essential for debugging and displaying information. Alongside this, comments are crucial for writing clear, maintainable code. This article breaks down the foundational uses of the print() function and the purpose of comments in Python. 1. Simple Output: The Classic Greeting Title: Printing a Single String Brief Definition This is the most fundamental use of the print() function. It takes a single string of text enclosed in quotes and displays it directly to the console. Practical Python Code print("Hello World!") Code Description print() : This is the built-in function that instructs Python to output data. ("...") : Everything inside the parentheses is the argument passed to the function. "Hello World!" : This is a string literal (text da...
Read more

What is Python?

Image
What is Python? A Beginner's Introduction  Watch the lesson tutorial   🔻 Python is a high-level, interpreted, general-purpose programming language known for its readability and versatility. 🔑 Key Characteristics of Python These features are what make Python so popular, especially for beginners: Interpreted: Python code is executed line-by-line by an interpreter at runtime, unlike compiled languages (like C++ or Java) which are translated into machine code before execution. This makes the development process faster and debugging easier. High-Level: It abstracts away complex details of the computer's architecture (like memory management), allowing you to write code that is closer to human language . General-Purpose: Python isn't specialized for one task; it can be used for a wide variety of applications, from web development to data analysis. Dynamically Typed: You don't need to declare the variable type (like integer, string, etc.) explicitly. The type is checke...
Read more

Set Up an Environment to Code in Python

Image
How to Set Up an Environment to Code in Python Watch the lesson tutorial   🔻 Before we start coding in Python, we need a proper coding environment . This makes it easy to write, run, and test your Python programs. Let’s see two main ways to create your Python coding setup — using PyCharm (a desktop IDE) and Replit (an online console). 🖥️ Option 1: Install PyCharm (Desktop IDE) PyCharm is one of the most popular Python editors created by JetBrains. It has features like auto-suggestions, debugging tools, and project management — perfect for beginners and professionals. Steps to Install PyCharm: Go to the official website: 🔗 https://www.jetbrains.com/pycharm/download Choose your operating system (Windows, macOS, or Linux). Download the Community Edition (it’s free). After installation, open PyCharm and create a New Project . Make sure Python is installed on your system. If not, download Python from here: 🔗 https://www.python.org/downloads/ Select ...
Read more