Python – Append content of one text file to another

Having two file names entered by users, the task is to append the content of the second file to the content of the first file with Python.

Append the content of one text file to another

• Using file object
• Using shutil module
• Using fileinput module

Suppose the text files file1.txt and file2.txt contain the following data.

file1.txt

file2.txt

Append the content of one text file to another using the file object

Enter the names of the files then open both files in read-only mode using the open() function and print the contents of the files before appending them using the read() function now close both files using the close() function. and open the first file in append mode and the second file in read mode. Append the contents of the second file to the first file using the write() function. Reposition the cursor of the files at the beginning using the seek() function. Print the contents of the appended files. and Close both files.

python3

# entering the file names
firstfile = input("Enter the name of first file ")
secondfile = input("Enter the name of second file ")

# opening both files in read only mode to read initial contents
f1 = open(firstfile, 'r')
f2 = open(secondfile, 'r')

# printing the contents of the file before appending
print('content of first file before appending -', f1.read())
print('content of second file before appending -', f2.read())

# closing the files
f1.close()
f2.close()

# opening first file in append mode and second file in read mode
f1 = open(firstfile, 'a+')
f2 = open(secondfile, 'r')

# appending the contents of the second file to the first file
f1.write(f2.read())

# relocating the cursor of the files at the beginning
f1.seek(0)
f2.seek(0)

# printing the contents of the files after appendng
print('content of first file after appending -', f1.read())
print('content of second file after appending -', f2.read())

# closing the files
f1.close()
f2.close()

Output:

Time complexity: O(n), where n is the total number of characters in both files.
Auxiliary space: O(1), since we are not using any additional data structures and are only reading and writing to the files.

Append the content of one text file to another using the using shutil module

we first open (file1) and after it, we open (file2) we open file one in read mode and file2 in append mode then copyfileobj() the function reads data from file1 in chunks and appends it to file2 until the entire content is copied.

Python3

import shutil

def append_files_method2(file1_path, file2_path):
    with open(file1_path, 'r') as file1:
        with open(file2_path, 'a') as file2:
            shutil.copyfileobj(file1, file2)

# Example usage:
file1_path = 'file1.txt'
file2_path = 'file2.txt'
append_files_method2(file1_path, file2_path)

Output:

Time complexity: O(n)
Auxiliary space: O(1), since we are not using any additional data structures and are only reading and writing to the files.

Append the content of one text file to another using the using fileinput Module

We here first open the target file2 in append mode. Then, by using fileinput.input(), we open the source file1 in read mode and iterate over its lines. and then for every line in file1, we write it to file2 using the write() method. This way work perfectly with large file to read and write data from one text file to another

Python3

import fileinput

def append_files_method3(file1_path, file2_path):
    with open(file2_path, 'a') as file2:
        with fileinput.input(files=file1_path) as file1:
            for line in file1:
                file2.write(line)

# Example usage:
file1_path = 'file1.txt'
file2_path = 'file2.txt'
append_files_method3(file1_path, file2_path)

Output:

Time complexity: O(n), where n is the total number of characters in both files.
Auxiliary space: O(1)