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Append File

Zero-dependency Python snippets for appending content to files using the standard library.

4 snippets available in this sub-category.

Simple

Append string to file

file append write open

Append content to existing file without overwriting

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

Notes

  • Use 'a' mode to append to existing file
  • Creates new file if it doesn't exist
  • Adds content at the end of file

Append with newline

file append write newline

Append multiple lines with proper newlines

with open("file.txt", "a") as f:
    f.write("Line 1\n")
    f.write("Line 2\n")

Notes

  • Manually add newlines for line breaks
  • Each write() call adds to the end
  • Useful for building log files

Complex

Append with timestamp

file append timestamp datetime logging

Append messages with automatic timestamps

from datetime import datetime


def append_with_timestamp(filename, message):
    """Append message with timestamp to file."""
    timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
    with open(filename, "a") as f:
        f.write(f"[{timestamp}] {message}\n")


append_with_timestamp("log.txt", "User logged in")

Notes

  • Automatically adds timestamps to entries
  • Useful for log files and activity tracking
  • Consistent timestamp format
  • Easy to parse later

Append with rotation

file append rotation size backup

Append with automatic file rotation based on size

import os
from datetime import datetime


def append_with_rotation(filename, content, max_size_mb=10):
    """Append content with file size rotation."""
    # Check if file exists and get its size
    if os.path.exists(filename):
        size_mb = os.path.getsize(filename) / (1024 * 1024)
        if size_mb > max_size_mb:
            # Create backup with timestamp
            timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
            backup_name = f"{filename}.{timestamp}"
            os.rename(filename, backup_name)

    # Append content
    with open(filename, "a") as f:
        f.write(content + "\n")


append_with_rotation("app.log", "New log entry")

Notes

  • Prevents log files from growing too large
  • Creates timestamped backups
  • Configurable size limit
  • Useful for long-running applications

🔗 Cross-References

🏷️ Tags

file, append, write, text, lines, io

📝 Notes

  • Use open() with mode 'a' to append to files
  • Appending does not overwrite existing content
  • Useful for logs and incremental data