Python File Modes: r, w, a, x, b, and +

This guide explains file modes: r, w, a, x, b, and + through a focused Python example. You will learn the behavior to expect, why it matters in a real program, and how to recognize the common mistakes before applying it in your own project.

What You Will Learn

File mode r reads an existing file, w truncates or creates one, a appends, x exclusively creates a new one, b enables binary data, and + allows both reading and writing.

When and Why to Use It

The following example focuses on a practical use of File Modes: r, w, a, x, b, and +.

Step-by-Step Example

from pathlib import Path
from tempfile import TemporaryDirectory

with TemporaryDirectory() as directory:
    file_path = Path(directory) / "notes.txt"
    with file_path.open("x", encoding="utf-8") as output_file:
        output_file.write("First\n")
    with file_path.open("a", encoding="utf-8") as output_file:
        output_file.write("Second\n")
    print(file_path.read_text(encoding="utf-8"))

Understanding the Example

Exclusive create prevents accidental overwrite of a preexisting notes.txt. Append adds a second line without discarding the first.

Expected Output

First
Second

Important Behavior and Edge Cases

Using w+ or r+ without understanding the file cursor can overwrite existing bytes. Plan whether you need read, write or append first.

Try It Yourself

Explain the difference between wb and w for writing a PNG file versus a text note.

For file examples, use a dedicated practice directory or a temporary directory. Make sure you understand whether a call reads, creates, overwrites or appends before using it on important files.

Common Beginner Mistakes

• Using w+ or r+ without understanding the file cursor can overwrite existing bytes. Plan whether you need read, write or append first.
• Assuming the current working directory, encoding, filesystem contents or file permissions will be identical on every computer.
• Skipping the practice step and assuming the example covers every input. Test at least one normal case and one edge case relevant to this topic.

Key Takeaways

• File mode r reads an existing file, w truncates or creates one, a appends, x exclusively creates a new one, b enables binary data, and + allows both reading and writing.
• Exclusive create prevents accidental overwrite of a preexisting notes.txt.
• Apply the technique deliberately, checking its documented input requirements and failure behavior before integrating it into a larger project.