Appending to Files in Python

Appending to files is a common task in Python when you want to add content without overwriting existing data. Python provides an 'a' mode in the open() function to simplify this process.

Key Concepts

• Append Mode ('a'): Opens the file for writing; content is added at the end. Creates the file if it doesn't exist.
• Append and Read Mode ('a+'): Opens the file for both appending and reading.
• No Overwrite: Unlike write mode ('w'), append mode does not erase the existing content.
• File Pointer: In append mode, the file pointer is always at the end. Use seek() if reading is required before writing (in 'a+' mode).
• Use Cases: Logging, journaling, storing user data, maintaining running outputs, etc.

10 Python Examples for Appending to Files

Example 1: Basic append using 'a' mode

with open('log.txt', 'a') as file:
    file.write('New log entry\\n')

Example 2: Appending multiple lines

lines = ['Line 1\\n', 'Line 2\\n']
with open('notes.txt', 'a') as file:
    file.writelines(lines)

Example 3: Appending inside a loop

with open('data.txt', 'a') as file:
    for i in range(3):
        file.write(f'Item {i}\\n')

Example 4: Appending user input

text = input("Enter your note: ")
with open('notes.txt', 'a') as file:
    file.write(text + '\\n')

Example 5: Creating a file if it doesn't exist

with open('newfile.txt', 'a') as file:
    file.write('First line in a new file\\n')

Example 6: Using 'a+' to read and append

with open('combined.txt', 'a+') as file:
    file.seek(0)
    print("Current content:\\n", file.read())
    file.write('Appended after reading\\n')

Example 7: Append with a timestamp

from datetime import datetime

with open('timelog.txt', 'a') as file:
    file.write(f"{datetime.now()}: Task done\\n")

Example 8: Append structured data (CSV-style)

name, score = 'John', 95
with open('scores.csv', 'a') as file:
    file.write(f'{name},{score}\\n')

Example 9: Append error logs in exception handling

try:
    result = 10 / 0
except ZeroDivisionError as e:
    with open('errors.log', 'a') as file:
        file.write(f"Error: {e}\\n")

Example 10: Append a blank line for separation

with open('summary.txt', 'a') as file:
    file.write('\\n')  # Adds a blank line