Python Program to Append to a File

Introduction

Appending data to a file is a common task when you want to add information to an existing file without overwriting its contents. Python makes it easy to append data to a file using the built-in functions. This tutorial will guide you through creating a Python program that appends data to a file.

Example:

Existing File Content (example.txt):
```
Hello, World!
```
Data to Append:
```
This line is appended to the file.
```

Resulting File Content:

Hello, World!
This line is appended to the file.

Problem Statement

Create a Python program that:

Opens a file in append mode.
Appends a specified string or multiple lines of text to the file.
Closes the file after appending.

Solution Steps

Specify the File Name: Provide the name of the file to which data will be appended.
Open the File: Use the open() function to open the file in append mode.
Append Data to the File: Use the write() or writelines() method to append data to the file.
Close the File: Ensure the file is properly closed after appending.

Python Program

# Python Program to Append to a File
# Author: https://www.rameshfadatare.com/

# Step 1: Specify the file name
file_name = "example.txt"

# Step 2: Open the file in append mode
try:
    with open(file_name, "a") as file:  # "a" mode is for appending
        # Step 3: Append data to the file
        file.write("This line is appended to the file.\n")
        
        # Optionally, append multiple lines at once using writelines()
        lines = [
            "Line 1: Appending to files is simple.\n",
            "Line 2: Just open the file in append mode.\n"
        ]
        file.writelines(lines)
        
    # File is automatically closed after exiting the with block
    print(f"Data successfully appended to '{file_name}'.")
    
except IOError:
    print(f"An error occurred while appending to the file '{file_name}'.")

Explanation

Step 1: Specify the File Name

The variable file_name is assigned the name of the file to which the data will be appended. If the file does not exist, Python will create it.

Step 2: Open the File in Append Mode

The open() function is used to open the file in append mode ("a"). The with statement ensures that the file is automatically closed after appending, even if an error occurs.

Step 3: Append Data to the File

The write() method is used to append a string to the file. The newline character (\n) is added to move to the next line.
The writelines() method can be used to append a list of strings to the file, where each string represents a line.

Step 4: Close the File

The file is automatically closed when exiting the with block. This is important to ensure that all data is properly saved and that the file is not left open.

Step 5: Handle Exceptions

The program includes exception handling using a try-except block to catch and handle any errors that may occur while appending to the file, such as IOError.

Output Example

Example Output (Program Console):

Data successfully appended to 'example.txt'.

Example File Content (example.txt):

Hello, World!
This line is appended to the file.
Line 1: Appending to files is simple.
Line 2: Just open the file in append mode.

Additional Examples

Example 1: Appending Multiple Lines from User Input

# Appending multiple lines from user input
file_name = "user_append.txt"

try:
    with open(file_name, "a") as file:
        while True:
            user_input = input("Enter text to append to the file (or type 'exit' to finish): ")
            if user_input.lower() == 'exit':
                break
            file.write(user_input + "\n")
    print(f"User input successfully appended to '{file_name}'.")
    
except IOError:
    print(f"An error occurred while appending to the file '{file_name}'.")

Output:

User enters text, and it is appended to user_append.txt until they type ‘exit’.

Example 2: Appending a List of Numbers to a File

# Appending a list of numbers to a file
file_name = "numbers_append.txt"

try:
    with open(file_name, "a") as file:
        numbers = [6, 7, 8, 9, 10]
        for number in numbers:
            file.write(f"Number: {number}\n")
    print(f"Numbers successfully appended to '{file_name}'.")
    
except IOError:
    print(f"An error occurred while appending to the file '{file_name}'.")