Python Programming! File Handling | Lectures 15

Let’s Start Python Programming for Beginners to Advanced. File Handling, Lectures 15

Table of Contents

🐍 Lecture 15: File Handling

🎯 Goal

By the end of this lecture, you will:

Understand how to read from and write to files in Python.
Be able to use open(), read(), write(), and with statements.
Practice saving game data, logs, or user info to a file.
Build a simple program that saves and loads text.

🧠 What Is File Handling?

So far, all the data we’ve worked with disappears when the program ends.
File handling lets us save data permanently on our computer, like saving a game, keeping a log, or storing notes.

📂 Think of it like writing in a notebook:

Writing → Saving to a file
Reading → Loading from a file

🔓 Opening Files with `open()`

To work with a file, we use the open() function.

Syntax:

file = open("filename.txt", "mode")

The mode tells Python what we want to do:

Mode	Meaning
`"r"`	Read (file must exist)
`"w"`	Append (adds to end of the file)
`"a"`	Append (adds to the end of the file)
`"r+"`	Read and write

💾 Writing to a File

Let’s create a file and write some text into it.

Example:

file = open("message.txt", "w")
file.write("Hello, world!")
file.close()

This creates a file called message.txt and writes "Hello, world!" inside.

📝 Note: If the file already exists, "w" will overwrite it.

📖 Reading from a File

Now let’s read what’s inside that file.

Example:

file = open("message.txt", "r")
content = file.read()
print(content)
file.close()

👉 Output:

Hello, world!

🛡️ Better Way: Using `with` Statement

Using with is safer and cleaner because it automatically closes the file for you.

Writing with `with`:

with open("log.txt", "w") as f:
    f.write("Game started\n")
    f.write("Player name: Alice")

Reading with with:

with open("log.txt", "r") as f:
    print(f.read())

➕ Appending to a File

Use "a" mode to add more text without deleting what’s already there.

with open("log.txt", "a") as f:
    f.write("\nGame ended")

Now log.txt will have:

Game started
Player name: Alice
Game ended

📋 Reading Line by Line

Sometimes, you want to read one line at a time.

Example:

with open("log.txt", "r") as f:
    for line in f:
        print("Line:", line.strip())

.strip() removes extra spaces or newline characters.

🧪 Try It Yourself!

Write a program that:

Asks the user to enter a message.
Saves it to a file called user_message.txt.
Then reads and prints the message back.

💡 Sample Code:

msg = input("Enter a message: ")

# Save to file
with open("user_message.txt", "w") as f:
    f.write(msg)

# Read from file
with open("user_message.txt", "r") as f:
    print("You saved:", f.read())

🚀 Challenge (Optional)

Make a simple diary app where the user can:

Add an entry (appended to a file).
View all entries (read from the file).

Example:

while True:
    action = input("What do you want to do? (add/view/quit): ").lower()

    if action == "add":
        entry = input("Write your diary entry: ")
        with open("diary.txt", "a") as f:
            f.write(entry + "\n---\n")
    elif action == "view":
        try:
            with open("diary.txt", "r") as f:
                print(f.read())
        except FileNotFoundError:
            print("No diary entries yet.")
    elif action == "quit":
        print("Goodbye!")
        break
    else:
        print("Invalid choice.")

🧒 Kids Corner

🧠 Imagine your robot has a notebook where it remembers everything you say.
Every time you talk, it writes it down — and when you ask, it reads it back to you!

🤖 Robot says: