How to Safely Handle File Reading and Writing Errors in Python

Reading and writing files is a fundamental part of many Python programs. However, it’s common to run into errors when working with files — especially if the file doesn’t exist, can’t be opened, or lacks the proper permissions.

These issues can cause your code to crash unexpectedly.

Thankfully, Python provides clear ways to safely handle these scenarios. If you’ve ever been confused by file-related errors, this guide will walk you through the most common causes and how to fix them safely and effectively.

What Causes This Error?

Here are a few typical reasons file read/write errors occur:

• File Not Found: Trying to open a file that doesn’t exist leads to a FileNotFoundError.
• Permission Denied: You may lack write or read access to the file or folder, causing a PermissionError.
• Incorrect File Mode: Attempting to read a file in write-only mode or vice versa triggers an error.
• File is Already Open Elsewhere: Another program locking the file can sometimes cause access problems.

Each of these errors can be handled gracefully using Python’s tools.

How to Fix It

1. Use Try/Except Blocks

Explanation: This approach lets you catch and handle file-related errors without crashing your program.

try:
    with open("data.txt", "r") as f:
        content = f.read()
except FileNotFoundError:
    print("The file was not found.")
except PermissionError:
    print("Permission denied when accessing the file.")

Why it works: You define specific exceptions to handle expected errors, avoiding program failure.

2. Check if File Exists Before Opening

Explanation: This avoids trying to read a file that may not be there.

import os

if os.path.exists("data.txt"):
    with open("data.txt", "r") as f:
        content = f.read()
else:
    print("File does not exist.")

Why it works: You verify the file’s presence before attempting to open it.

3. Use Safe File Writing with Context Managers

Explanation: Using with ensures files are properly closed, even if an error occurs.

try:
    with open("output.txt", "w") as f:
        f.write("Saving some important data.")
except Exception as e:
    print(f"An error occurred: {e}")

Why it works: with manages file lifecycle safely, and the catch-all error helps with debugging.

Real Example

Here’s a sample script that demonstrates a common error:

# Faulty code
f = open("nonexistent.txt", "r")
data = f.read()
f.close()

This code will raise a FileNotFoundError if the file doesn’t exist.

Fixed version:

try:
    with open("nonexistent.txt", "r") as f:
        data = f.read()
except FileNotFoundError:
    print("The file does not exist. Please check the file name or path.")

Now the error is caught and handled gracefully.

Tips to Prevent This Error

• Always use try/except when working with files.
• Check for file existence using os.path.exists() or pathlib.Path.exists().
• Use context managers (with open(...)) to avoid forgetting to close files.

Conclusion

File read/write errors can be frustrating, especially when they crash your program unexpectedly. The good news is that Python makes it easy to handle them safely with simple techniques.

By using try/except, checking for file existence, and adopting context managers, you’ll write more robust code.

Bookmark this guide as a quick reference the next time you’re working with files.