How to Write to a File in Python

What you’ll build or solve

You’ll write text to a file in Python using safe, common patterns.

When this approach works best

Writing to a file works well when you:

• Save results from a script, like a report, logs, or processed data.
• Store user-generated content, like notes or exported text.
• Keep a simple record of events, like timestamps, errors, or progress updates.

Avoid this approach when you need many updates to the same data or concurrent writes from multiple processes. Use a database or a logging system designed for that.

Prerequisites

• Python installed
• You know what files and folders are on your computer

Step-by-step instructions

1) Open a file in the right mode

Use with open(...) so Python closes the file automatically.

Option A (most common): Overwrite with "w"

Creates the file if it does not exist. Replaces the file contents if it does.

with open("output.txt", "w", encoding="utf-8") as f:
    f.write("Hello!\n")

Option B: Append with "a"

Creates the file if it does not exist. Adds new content to the end.

with open("output.txt", "a", encoding="utf-8") as f:
    f.write("Another line.\n")

What to look for: "w" clears the file first. Use "a" when you want to keep what’s already there. For portable file paths, see Example 4.

2) Write text in one go or line by line

Use write() for a single string. Use writelines() when you already have a list of strings.

Option A: Write a single string

message = "First line\nSecond line\n"

with open("output.txt", "w", encoding="utf-8") as f:
    f.write(message)

Option B: Write many lines

lines = ["First line\n", "Second line\n", "Third line\n"]

with open("output.txt", "w", encoding="utf-8") as f:
    f.writelines(lines)

What to look for: writelines() does not add \n for you. Put newline characters into each line.

3) Handle file errors without crashing

Catching errors helps when the folder is read-only, the path is wrong, or permissions block writing.

try:
    with open("output.txt", "w", encoding="utf-8") as f:
        f.write("Writing safely.\n")
except PermissionError:
    print("No permission to write here. Try a different folder.")
except FileNotFoundError:
    print("Folder not found. Check the path.")

Examples you can copy

Example 1: Save a simple report

report = [
    "Daily Report\n",
    "-----------\n",
    "Users: 120\n",
    "Signups: 18\n",
]

with open("report.txt", "w", encoding="utf-8") as f:
    f.writelines(report)

Example 2: Append log lines with timestamps

from datetime import datetime

timestamp = datetime.now().isoformat(timespec="seconds")
line = f"{timestamp} - job started\n"

with open("app.log", "a", encoding="utf-8") as f:
    f.write(line)

Example 3: Write cleaned lines to a new file

cleaned = []

with open("raw.txt", "r", encoding="utf-8") as f:
    for line in f:
        line = line.strip()
        if line:
            cleaned.append(line + "\n")

with open("cleaned.txt", "w", encoding="utf-8") as f:
    f.writelines(cleaned)

Example 4: Write a file next to your script with pathlib

This example builds a path that works even when you run the script from a different folder.

from pathlib import Path

out_path = Path(__file__).with_name("output.txt")

with out_path.open("w", encoding="utf-8") as f:
    f.write("This file lives next to the script.\n")

Example 5: Create a folder before writing

from pathlib import Path

folder = Path("exports")
folder.mkdir(parents=True, exist_ok=True)

file_path = folder / "results.txt"

with file_path.open("w", encoding="utf-8") as f:
    f.write("Saved in exports/results.txt\n")

Common mistakes and how to fix them

Mistake 1: Using "w" and accidentally overwriting a file

What you might do:

with open("output.txt", "w", encoding="utf-8") as f:
    f.write("New content\n")

Why it breaks: "w" clears the file first, so you lose what was already there.

Correct approach:

with open("output.txt", "a", encoding="utf-8") as f:
    f.write("New content\n")

Mistake 2: Forgetting newline characters

What you might do:

lines = ["one", "two", "three"]

with open("output.txt", "w", encoding="utf-8") as f:
    f.writelines(lines)

Why it breaks: All text runs together because Python does not add line breaks for you.

Correct approach:

lines = ["one\n", "two\n", "three\n"]

with open("output.txt", "w", encoding="utf-8") as f:
    f.writelines(lines)

Mistake 3: Writing to a different folder than you expect

What you might do:

with open("output.txt", "w", encoding="utf-8") as f:
    f.write("Where did this go?\n")

Why it breaks: Relative paths write to the current working directory, which can differ between your IDE and terminal.

Correct approach:

from pathlib import Path

file_path = Path(__file__).with_name("output.txt")

with file_path.open("w", encoding="utf-8") as f:
    f.write("Now it’s next to the script.\n")

Troubleshooting

If you see PermissionError, try writing to a folder you own, like your home directory, or choose a different output path.

If you see FileNotFoundError, the folder in the path does not exist. Create it first, as shown in Example 5.

If you can’t find the file, print the working directory:

import os
print(os.getcwd())

If your file has strange characters, set encoding="utf-8" when writing and reading.

If you see missing lines in a log, check that you used "a" for append and included \n.

Quick recap

• Open files with with open(...) so they close automatically.
• Use "w" to overwrite and "a" to append.
• Use write() for one string and writelines() for many lines.
• Catch PermissionError and missing-folder errors when writing.
• Use pathlib when you need a predictable output location.