Python File Append — Full Cheat Sheet

What is File Appending?

Appending means adding new text to the end of a file without deleting the existing data. The "a" mode opens the file for appending.

Append Mode Properties

• a — Opens file for appending
• Does NOT erase existing content
• Writes at the end of the file only
• If file does not exist → creates a new file automatically

Basic Append Example

f = open("demofile.txt", "a")
f.write("This text is appended!")
f.close()

Append a New Line

Use "\\n" to add a new line before writing.

with open("notes.txt", "a") as f:
  f.write("\nNew line added.")

Append Multiple Lines

Use writelines() to append a list of strings.

lines = [
  "Line A" + "\n",
  "Line B" + "\n"
]

with open("demo.txt", "a") as f:
  f.writelines(lines)

Append Can Create a File

Unlike "w" mode, append only adds to the file and will not erase anything. If the file is missing, Python creates it.

# If the file does not exist, "a" mode will create it
f = open("newfile.txt", "a")
f.write("Created automatically using append!")
f.close()

Summary

• a: Append mode — adds to file
• a+: Append + read mode
• write(): writes text at end
• writelines(): writes list of strings
• with open(): best practice (auto-closes file)
• Append mode never deletes old data