DEV Community: still-purrfect

Working With .txt Files in Python: Simple but Powerful

still-purrfect — Mon, 08 Jun 2026 13:38:35 +0000

Not every file is complex.
Sometimes, all you need is a simple text file.
And that’s exactly where .txt files come in.
With file handling, we’ve learned how Python can read and write data.
Now let’s make it more practical by focusing on one of the simplest and most commonly used file types: .txt files.
A .txt file is just a plain text file. No formatting, no special structure just raw text.

🔹 Writing to a .txt File

file = open("notes.txt", "w")

file.write("This is my first text file.")

file.close()

This creates a file called notes.txt and writes content into it.

🔹 Reading from a .txt File

file = open("notes.txt", "r")

content = file.read()
print(content)

file.close()

This reads everything inside the file.

🔹 Adding More Content

file = open("notes.txt", "a")

file.write("\nThis is a new line.")

file.close()

This adds new content without deleting what was already there.

🔹 Using "with" (Better Practice)

Instead of manually closing files, Python gives a cleaner way:

with open("notes.txt", "r") as file:
    content = file.read()
    print(content)

This automatically handles closing the file.

💡 Why .txt Files Matter

.txt files are simple, but very useful:

Storing notes
Saving logs
Writing simple data
Testing file handling concepts They are often the starting point before moving into more complex file types like CSV or databases.

🌱 Challenge

Create a program that:

Writes your name and a short message into a .txt file
Reads the file and prints the content
Adds another line to the file. Keep it simple and focus on understanding the flow.

Next, we’ll move into exception handling, where your program learns how to deal with errors when working with files and user input.

Inheritance in Python: Building Code That Grows With You

still-purrfect — Mon, 08 Jun 2026 09:05:54 +0000

What if you didn’t have to rewrite code every time you wanted something similar?
What if you could build on what already exists?
That’s exactly what inheritance does.
So far, we’ve learned how to create classes and objects, and how they help us model real-world things in code.
Now we take it one step further: inheritance.
Inheritance allows one class to use the properties and methods of another class.
In simple terms, it means: build once, reuse and extend.

🔹 The Parent Class

A parent class is the original class.

class Animal:
    def speak(self):
        print("Animal makes a sound")

🔹 The Child Class

A child class inherits from the parent class.

class Dog(Animal):
    pass

dog1 = Dog()
dog1.speak()

Even though Dog has no method of its own, it can still use speak() from Animal.

🔹 Overriding Methods

A child class can also change how a method works.

class Dog(Animal):
    def speak(self):
        print("Dog barks")

dog1 = Dog()
dog1.speak()

Now the child class replaces the parent behavior.

💡 Why Inheritance Matters

Inheritance helps you:

Reuse code instead of repeating it
Organize programs better
Build scalable systems
Represent real-world relationships In real applications, inheritance is used in everything from games to banking systems. It helps code grow without becoming messy.

🌱 Final Challenge

Create:

A parent class called Vehicle with a method move()
A child class called Car that inherits from Vehicle
Override the move() method in Car to print something different Then create an object of Car and call the method.

🎯 Final Note

If you’ve followed all the topics in this series, you now understand the foundation of programming from basic data to object-oriented thinking.

This is the point where you stop just learning syntax… and start thinking like a developer.

Sets in Python: Working With Unique Values

still-purrfect — Mon, 08 Jun 2026 08:59:04 +0000

Have you ever had duplicate data and wished you could just remove repeats automatically?
That’s exactly what sets do.
So far, we’ve worked with lists, tuples, dictionaries, and other data types.
Now we’re looking at something simpler but very powerful: sets.
A set is a collection of items that does not allow duplicates.

🔹 Creating a Set

numbers = {1, 2, 3, 4, 5}
print(numbers)

Sets use curly brackets, just like dictionaries but they only store values.

🔹 Removing Duplicates Automatically

numbers = {1, 2, 2, 3, 4, 4, 5}
print(numbers)

Output:
{1, 2, 3, 4, 5}
Duplicates are automatically removed.

🔹 Adding Items to a Set

numbers = {1, 2, 3}

numbers.add(4)

print(numbers)

🔹 Removing Items

numbers = {1, 2, 3, 4}

numbers.remove(2)

print(numbers)

💡 Why Sets Matter

Sets are useful when you need:

Unique values only
Fast membership checks
Cleaned-up data They are often used in:
Data cleaning
Removing duplicates from lists
Comparing groups of items

Think of sets as a “no repetition allowed” container.

🌱 Challenge

Write a program that:

Creates a list with repeated numbers
Converts it into a set
Prints the cleaned unique values

Bonus: Try adding a new number to the set and printing it again.

Next, we’ll explore inheritance, where you learn how classes can build on each other like real systems in software development.

Date and Time in Python: Working With Real-World Moments

still-purrfect — Mon, 08 Jun 2026 08:52:46 +0000

Every app you use alarms, calendars and reminders depends on one thing:
Time.
So far, we’ve learned how to write programs that store data, make decisions, handle errors, and work with files.
Now we move into something more practical: date and time.
Python allows us to work with time using the built-in datetime module.

🔹 Getting the Current Date and Time

import datetime

now = datetime.datetime.now()
print(now)

This prints the current date and time from your system.

🔹 Working with Dates Only

Sometimes you only need the date.

import datetime

today = datetime.date.today()
print(today)

This gives only the current date.

🔹 Creating Your Own Date

You can also create a specific date.

import datetime

birthday = datetime.date(2000, 5, 17)
print(birthday)

🔹 Formatting Date and Time

Raw date formats can look messy, so we format them.

import datetime

now = datetime.datetime.now()

print(now.strftime("%Y-%m-%d"))

This gives a clean format like:
2026-06-08

💡 Why Date and Time Matter

Date and time are used in:

Reminders ⏰
Scheduling apps 📅
Login systems 🔐
Logs in applications 📊
Automated tasks 🤖 Almost every real system tracks time in some way. Without it, apps would feel static and unorganized.

🌱 Challenge

Write a program that:

Displays today’s date
Asks the user for their birth year
Calculates their age Bonus: Format the output in a clean sentence.

Next, we’ll explore sets, where you learn how to store unique values and remove duplicates automatically.

Exception Handling in Python: Making Your Code Fail Safely

still-purrfect — Mon, 08 Jun 2026 08:45:23 +0000

What happens when your program runs into an error?
Without preparation… it just stops.
And that’s not something real applications can afford.
So far, we’ve learned how to write programs that store data, make decisions, repeat actions, and even work with files.
But in real life, things don’t always go as expected.
Users enter wrong input, files may be missing, or calculations may fail.
That’s where exception handling comes in.

🔹 What is an Exception?

An exception is an error that occurs while a program is running.
For example:

print(10 / 0)

This causes an error because you cannot divide by zero.
Without handling it, the program crashes immediately.

🔹 Using Try and Except

Python allows us to handle errors using try and except.

try:
    print(10 / 0)
except:
    print("Something went wrong")

Instead of crashing, the program handles the error gracefully.

🔹 Handling Specific Errors

You can also handle specific types of errors.

try:
    number = int(input("Enter a number: "))
    print(10 / number)
except ZeroDivisionError:
    print("You cannot divide by zero")
except ValueError:
    print("Please enter a valid number")

Now the program knows exactly what went wrong.

🔹 Finally Block

There is also a finally block that always runs.

try:
    print("Trying something...")
except:
    print("Error occurred")
finally:
    print("This will always run")

This is often used for cleanup actions like closing files.

💡 Why Exception Handling Matters

Exception handling makes your program:

More stable
More user-friendly
Less likely to crash
Ready for real-world use In real applications, errors are not avoided they are managed.

🌱 Challenge

Write a program that:

Asks the user to enter a number
Divides 100 by that number
Handles:
- Zero division error
- Invalid input error Make sure your program never crashes, no matter what is entered.

Next, we’ll explore date and time, where your programs learn how to work with real-world time-based data like schedules and timestamps.

File Handling in Python: Working With Real Data

still-purrfect — Mon, 08 Jun 2026 08:32:37 +0000

So far, everything we’ve done exists only inside the program.
But what if your program could remember things even after it closes?
That’s where file handling comes in.
So far, we’ve worked with variables, functions, and modules.
But in real applications, data doesn’t just disappear when a program stops running.
It is saved in files like .txt, .csv, or databases.
Python allows us to work with these files using file handling.

🔹 Opening a File

To work with a file, we first open it using open().

file = open("file.txt", "r")

The "r" means read mode (we are only reading the file).

🔹 Reading a File

Once the file is open, we can read its content.

file = open("file.txt", "r")

content = file.read()
print(content)

file.close()

Always remember to close the file after using it.

🔹 Writing to a File

We can also create or write into files using "w" mode.

file = open("file.txt", "w")

file.write("Hello, this is my first file.")

file.close()

⚠️ Note: Writing mode will overwrite existing content.

🔹 Appending to a File

If you don’t want to overwrite, use "a" mode.

file = open("file.txt", "a")

file.write("\nThis is an additional line.")

file.close()

This adds new content without deleting old data.

💡 Why File Handling Matters

File handling allows your programs to:

Save user data
Store results
Keep records
Work like real applications Without it, everything resets once the program stops. With it, your program can actually remember things.

🌱 Challenge

Create a program that:

Writes your name and age into a file
Opens the file again
Reads and prints the content Try also appending a new line after that.

Next, we’ll explore exception handling, where your program learns how to handle errors without crashing.

Modules in Programming: Using and Organizing Code Like a Pro

still-purrfect — Mon, 08 Jun 2026 08:22:43 +0000

What if you didn’t have to write everything from scratch every time you code?
That’s exactly what modules help you do.
So far, we’ve learned how to write functions and even shorten them using lambda functions.
But as programs grow, keeping everything in one file becomes messy.
That’s where modules come in.
A module is simply a file that contains Python code functions, variables, or classes that you can reuse in other programs.

🔹 Using Built-in Modules

Python already comes with ready made modules.
For example, the math module:

import math

print(math.sqrt(16))

This calculates the square root of 16.
Instead of writing the logic yourself, you just use what already exists.

🔹 Importing Specific Features

Sometimes you don’t need the whole module just one part.

from math import sqrt

print(sqrt(25))

This imports only the square root function.

🔹 Creating Your Own Module

You can also create your own module.
Imagine you have a file called my_functions.py:

def greet(name):
    return "Hello " + name

Now you can use it in another file:

import my_functions

print(my_functions.greet("Mary"))

🔹 Why Modules Matter

Modules help you:

Organize your code
Reuse functions easily
Keep programs clean
Work on bigger projects without confusion In real development, no one writes everything in one file. Modules make large systems manageable.

🌱 Challenge

Import the math module
Use it to:
- Find the square root of 49
- Find the value of pi (math.pi)
Then create your own module with a function that:
- Takes a name
- Returns a greeting Try importing it into another file and using it.

Next, we’ll explore file handling, where your programs start working with real files like .txt just like real applications do.

Lambda Functions in Programming: Short, Simple, and Powerful

still-purrfect — Mon, 08 Jun 2026 08:12:08 +0000

Sometimes you don’t need a full function… just a quick one-liner.
That’s exactly what lambda functions are for.
So far, we’ve learned how to create functions using def.
Those are great for larger tasks.
But in programming, there are moments where you need something very small, very fast, and temporary.
That’s where lambda functions come in.
A lambda function is a short way of writing a function in a single line.

🔹 Basic Lambda Function

Instead of writing a full function like this:

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

You can write it using lambda:

add = lambda a, b: a + b

print(add(3, 5))

Same result. Less code.

🔹 How It Works

A lambda function:

Has no name (or a temporary one)
Is written in one line
Is used for simple tasks Structure:

lambda arguments: expression

🔹 Example: Multiply Numbers

multiply = lambda x, y: x * y

print(multiply(4, 6))

🔹 When to Use Lambda

Lambda functions are useful when:

You need a small function quickly
You don’t want to define a full function
You are working with built-in functions like map() or filter() (we’ll get there later)

💡 Why Lambda Matters

Lambda functions are not about replacing normal functions.
They are about simplicity.
They help you write cleaner code when the task is small and straightforward.
Think of them as shortcuts not replacements.

🌱 Challenge

Write a lambda function that:

Takes one number
Returns the square of that number Then:
Test it with at least 3 different numbers Try also writing the same thing using a normal function and compare the two.

Next, we’ll explore modules, where you learn how to use code written by other people and organize your own like a real project.

Functions in Programming: Writing Code Once, Using It Anytime

still-purrfect — Mon, 08 Jun 2026 08:03:56 +0000

What if you never had to rewrite the same code twice?
That’s exactly what functions help you do.
So far, we’ve worked with data, logic, repetition, and text.
But as programs grow, writing everything step by step becomes messy.
That’s where functions come in.
A function is a block of code that performs a specific task. You define it once, and reuse it whenever needed.

🔹 Creating a Function

In Python, we use the keyword def to define a function.

def greet():
    print("Hello, welcome!")

To use it, we call it:

greet()

🔹 Functions with Parameters

Functions become more powerful when they can accept input.

def greet(name):
    print("Hello " + name)

greet("Mary")

Now the function can work with different names.

🔹 Functions with Multiple Inputs

You can pass more than one value into a function.

def add_numbers(a, b):
    print(a + b)

add_numbers(5, 3)

This makes your code flexible and reusable.

🔹 Return Values

Sometimes you don’t just want to print a result you want to use it later.
That’s where return comes in.

def multiply(a, b):
    return a * b

result = multiply(4, 5)
print(result)

Now the result can be stored and reused.

💡 Why Functions Matter

Functions help you:

Avoid repeating code
Organize your program better
Make your code easier to read
Reuse logic anywhere in your program In real applications, functions are everywhere. Without them, programs would be long, messy, and hard to manage.

🌱 Challenge

Write a function that:

Takes a name and age as input
Prints a sentence like: “My name is ___ and I am ___ years old” Then:
Call the function at least 2 times with different values Try to think of it as building a small reusable tool.

Next, we’ll explore lambda functions, a shorter way of writing functions used in more advanced Python code.

Strings in Programming: Working With Text Like a Pro

still-purrfect — Mon, 08 Jun 2026 07:54:38 +0000

Everything you see on a screen messages, names, passwords, even emails is basically text.
In programming, that text is called a string.
So far, we’ve worked with numbers, logic, and repetition.
Now we move into something even more common in real applications: text data.
A string is simply a sequence of characters inside quotes.

name = "Mary"
print(name)

🔹 Creating Strings

Strings can be written using either single or double quotes:

text1 = "Hello"
text2 = 'World'

Both are valid. Just be consistent.

🔹 String Concatenation (Joining Text)

You can combine strings using the + operator.

first_name = "Mary"
last_name = "Akinyi"

print(first_name + " " + last_name)

This joins the two strings into one full name.

🔹 Accessing Characters

Strings are like a sequence of letters. Each character has a position (index).

word = "Python"

print(word[0])
print(word[1])

This prints:

Remember: indexing starts from 0.

🔹 String Length

You can find how long a string is using len().

word = "Python"
print(len(word))

This returns the number of characters in the string.

💡 Why Strings Matter

Strings are everywhere in programming:

User names
Messages
Input from users
Website content
Passwords

Almost every application depends on text in some way.
Understanding strings gives you control over how programs communicate.

🌱 Challenge

Write a program that:

Takes a first name and last name
Combines them into a full name
Prints how many characters the full name has Try to think about how strings are used in real applications, not just the example.

Next, we’ll explore functions, where you learn how to organize your code into reusable blocks like a real developer.

Loops in Programming: How to Make Your Code Repeat Without Stress

still-purrfect — Mon, 08 Jun 2026 07:40:20 +0000

Have you ever written the same code again and again and thought there must be a better way?
That’s exactly what loops solve.
So far, we’ve learned how to store data, make decisions using if statements, and work with operators.
But what if we want to repeat something multiple times?
Instead of writing the same code over and over, we use loops.
Loops allow your program to repeat a block of code as many times as needed.

🔹 1. For Loop

A for loop is used when you know how many times you want to repeat something.

for i in range(5):
    print("Hello")

This prints “Hello” 5 times.

🔹 2. While Loop

A while loop keeps running as long as a condition is true.

x = 1

while x <= 5:
    print(x)
    x = x + 1

This prints numbers from 1 to 5.

💡 Why Loops Matter

Loops save time and reduce repetition.
Without loops, you repeat code manually.
With loops, one line can do the work of many.
They are one of the most important tools in programming because they make your code efficient and scalable.

🌱 Challenge

Write a program that:

Prints numbers from 1 to 10
Then prints “Python is fun” 5 times

Try to do it using both:

a for loop
a while loop

Next, we’ll explore strings, where you learn how to work with text in a deeper and more practical way.

If Statements in Programming: Teaching Your Code to Decide

still-purrfect — Mon, 08 Jun 2026 07:33:11 +0000

So far, we’ve learned how to store data, organize it, and even perform operations using operators.
But most real programs don’t just run top to bottom.
They make decisions.
That’s where if statements come in.
An if statement allows your program to run certain code only when a condition is true.
Think of it like a simple decision:
“If this is true, do this. Otherwise, do something else.”

🔹 Basic If Statement

age = 18

if age >= 18:
    print("You are allowed to vote")

In this case, the program checks the condition age >= 18.
If it is true, it runs the message.
If not, it simply does nothing.

🔹 If...Else Statement

Sometimes we want two outcomes.

age = 16

if age >= 18:
    print("You are allowed to vote")
else:
    print("You are not allowed to vote")

Now the program chooses between two paths.
One for true, one for false.

🔹 If...Elif...Else

When there are multiple conditions, we use elif.

marks = 75

if marks >= 80:
    print("Grade A")
elif marks >= 60:
    print("Grade B")
else:
    print("Grade C")

The program checks conditions from top to bottom and stops once one is true.

💡 Why If Statements Matter

If statements are what make programs feel “intelligent.”
Without them, everything would run the same way every time.
With them, your program can:

React to input
Make decisions
Handle different situations This is the beginning of logic in programming.

🌱 Challenge

Write a program that:

Takes a number (your choice)
Checks if it is:
- Greater than 0 → print "Positive"
- Less than 0 → print "Negative"
- Equal to 0 → print "Zero" Try to think step by step. That’s how programming becomes easier.

Next, we’ll look at loops, where your program stops doing things once and starts repeating actions efficiently.