📁 Python File Handling – Read, Write, Append & Manage Files Easily

🧲 Introduction – Why File Handling Matters in Python

Handling files is essential for storing data permanently. Python’s built-in file handling functions make it easy to create, read, update, or delete files—supporting everything from configuration files and logs to data pipelines.

🎯 What You Will Learn:

• Opening, reading, and writing files using open()
• File modes: r, w, a, x, b, t, and +
• Functions like read(), write(), readlines(), writelines()
• Exception handling with try...except for file errors

📂 1. Opening and Closing Files

✅ Using open() Function

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

✅ Explanation:

• "r" opens the file in read mode.
• close() frees system resources and ensures changes are saved.

💡 Tip: Always close files manually or use a with block for auto-closure.

✅ Using with Statement (Best Practice)

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

✅ This ensures the file is closed automatically after the block ends.

🧾 2. File Modes in Python

📖 3. Reading from Files

✅ read()

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

✅ Reads entire file content as a string.

✅ readline()

with open("example.txt", "r") as f:
    print(f.readline())

✅ Reads one line at a time.

✅ readlines()

with open("example.txt", "r") as f:
    lines = f.readlines()
    print(lines)

✅ Returns a list of lines in the file.

✏️ 4. Writing to Files

✅ write()

with open("output.txt", "w") as f:
    f.write("Hello, World!\n")

✅ Writes a string to file. Must add \n for line breaks.

✅ writelines()

lines = ["Line 1\n", "Line 2\n"]
with open("output.txt", "w") as f:
    f.writelines(lines)

✅ Writes multiple strings (as list) into file.

➕ 5. Appending to Files

with open("output.txt", "a") as f:
    f.write("New Line\n")

✅ Adds content at the end without overwriting existing data.

❌ 6. Handling File Not Found Errors

try:
    with open("missing.txt", "r") as f:
        print(f.read())
except FileNotFoundError:
    print("File does not exist.")

✅ Prevents crash if file is missing by using try...except.

💡 Best Practices

• ✅ Use with open() for safety and simplicity.
• ✅ Choose correct file mode ('r', 'w', 'a') as per operation.
• ✅ Use os.path.exists() to check file presence (optional).
• ✅ Handle exceptions gracefully.

📌 Summary – Recap & Next Steps

Python file handling is crucial for working with persistent data sources. From reading logs to writing reports, it simplifies data access and manipulation.

🔍 Key Takeaways:

• Use open() with correct modes (r, w, a, x)
• Use read(), write(), readlines() for I/O
• Always use with open() to manage files efficiently
• Handle file-related errors with try...except

⚙️ Real-World Relevance:
This is widely used in data logging, report generation, configuration management, and automation.

❓ FAQ – Python File Handling

❓ How do I safely open and close a file in Python?

✅ Use:

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

This auto-closes the file.

❓ What’s the difference between w and a?

✅ 'w' overwrites the file; 'a' appends data at the end.

❓ How do I read a file line by line?

✅ Use readline() or a loop:

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

❓ How to handle missing file errors?

✅ Use try...except FileNotFoundError block.

❓ What’s the difference between text and binary mode?

✅ 't' is for human-readable text. 'b' is for non-text files like images or audio.