Welcome back to the Python Tutorial Series for Beginners! 🎉

In Lesson 12, we explored Modules and Packages and learned how to organize code and use external libraries.

Now in Lesson 13, we’ll dive into File Handling – an essential part of programming that allows you to read, write, and manage files on your computer.

By the end of this lesson, you’ll understand:

• Opening and closing files
• Reading files (read, readline, readlines)
• Writing and appending to files
• Working with file paths
• Using with open() (context managers)
• Handling file errors safely
• Beginner exercises

🔹 1. Why File Handling Matters

👉 File handling lets your programs store data permanently.

Examples in real life:

• Saving user data in a text file
• Logging program activity
• Reading CSV files for data analysis
• Writing results to files instead of printing them only

🔹 2. Opening a File

The built-in open() function is used:

# open(filename, mode)
file = open("example.txt", "r")

Common modes:

• "r" → Read (default)
• "w" → Write (overwrites file)
• "a" → Append (adds to file)
• "b" → Binary mode (for images, etc.)

Always remember to close the file:

file.close() 

🔹 3. Reading from a File

Assume example.txt contains:

Hello World
Python is awesome

Read entire content:

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

👉 Output:

Hello World
Python is awesome

Read only first 5 characters:

file = open("example.txt", "r")
print(file.read(5))
file.close()

👉 Output: Hello

Read line by line:

file = open("example.txt", "r")
print(file.readline())   # first line
print(file.readline())   # second line
file.close()

Read all lines into a list:

file = open("example.txt", "r")
lines = file.readlines()
print(lines)
file.close()

👉 Output:

['Hello World\n', 'Python is awesome\n'] 

🔹 4. Writing to a File

👉 Writing will overwrite existing content.

file = open("example.txt", "w")
file.write("New content here\n")
file.write("Another line\n")
file.close()

👉 Now example.txt contains:

New content here
Another line

🔹 5. Appending to a File

👉 Use "a" mode to keep existing content and add new lines.

file = open("example.txt", "a")
file.write("This line is appended.\n")
file.close()

🔹 6. Using with open() (Best Practice)

Instead of manually opening and closing, use a context manager:

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

✅ The file automatically closes after the block.

🔹 7. Working with File Paths

• If the file is in the same folder → just use "example.txt".
• If in another folder:

file = open("data/example.txt", "r") 

• For absolute paths (Windows):

file = open("C:\\Users\\User\\Documents\\example.txt", "r") 

🔹 8. Handling File Errors

Sometimes files don’t exist. Handle safely with try...except:

try:
   with open("notfound.txt", "r") as file:
       content = file.read()
       print(content)
except FileNotFoundError:
   print("File not found!")

👉 Output:

File not found! 

🔹 9. Real-World Use Cases

✅ Writing Logs

with open("log.txt", "a") as log:
   log.write("User logged in\n")

✅ Storing User Input

name = input("Enter your name: ")
with open("users.txt", "a") as f:
   f.write(name + "\n")
 

✅ Reading Config Files

with open("config.txt", "r") as cfg:
   settings = cfg.readlines()
   print("Settings:", settings)

🔹 10. Exercises for Beginners

Try these in a new file (lesson13.py):

1. Create a file named notes.txt and write three lines into it.
2. Read the file and print each line separately.
3. Append a new line to notes.txt saying “Python makes file handling easy!”.
4. Write a program that counts how many lines are in a file.
5. Use try...except to handle the case where a file does not exist.

🎯 Recap

In this lesson, you learned:
✅ How to open and close files in Python
✅ Reading (read, readline, readlines) and writing to files
✅ Difference between write (w) and append (a) modes
✅ Best practice with with open()
✅ Error handling with missing files

Next up: Lesson 14 – Error Handling & Exceptions in Python ⚠️