1. Introduction

In this tutorial, we will be exploring how to append new data to existing files and modify current data within files. This is an important skill to have as a programmer, as it allows you to effectively manage and manipulate data stored in files.

What You Will Learn:
- How to append data to an existing file
- How to modify data within a file

Prerequisites:
- Basic knowledge of programming concepts (variables, data types)
- Familiarity with any programming language (for this tutorial, we will use Python)

2. Step-by-Step Guide

Appending and modifying file data involves opening a file in a specific mode that allows you to make changes. In Python, you can open a file in append mode ('a') or write mode ('w').

• Append mode allows you to add data to the end of the file without deleting any existing data.
• Write mode allows you to overwrite the entire file with new data.

Best Practice: Always close the file after performing your operations. This will free up system resources and ensure changes are saved.

3. Code Examples

Example 1: Appending data to a file

# Open the file in append mode
file = open('example.txt', 'a')

# Write new data
file.write('This is appended text.\n')

# Close the file
file.close()

Example 2: Modifying data in a file

Modifying data within a file is a bit more involved, as it requires reading the file, changing the data, and writing it back.

# Open the file in read mode
file = open('example.txt', 'r')

# Read the file data
data = file.readlines()

# Close the file after reading
file.close()

# Modify the data
data[1] = 'This is modified text.\n'

# Open the file in write mode and overwrite it with the modified data
file = open('example.txt', 'w')
file.writelines(data)

# Close the file
file.close()

4. Summary

In this tutorial, you learned how to append data to existing files and modify data within files using Python. The key points to remember are the different file modes ('a' for append, 'w' for write), and the importance of closing a file after use.

Next Steps: Further your learning by exploring other file operations, such as reading from files and deleting files.

Additional Resources: Python's official documentation on file I/O is a great resource for more in-depth information.

5. Practice Exercises

Exercise 1: Write a program that appends your name to a file named 'names.txt'.

Exercise 2: Write a program that replaces the first line of a file named 'text.txt' with 'This is a new first line.'.

Exercise 3: Write a program that appends a new line to a file for each item in a list.

Tips: Remember to close your files after use, and always open your files in the correct mode for the operation you want to perform.