Python Program to merge two files into a third file
Last Updated : 06 Sep, 2024
Reading and writing to a file. Let the given two files be file1.txt and file2.txt. Our Task is to merge both files into a third file say file3.txt. The following are steps to merge in Python.
Note: To successfully run the below program file1.txt and file2.txt must exist in the same folder. Suppose the text files file1.txt and file2.txt contain the following data.
Program to Merge two files into New File
Below are the methods that we will cover in this article:
file1.txt
file2.txt 
Naive Approach to merge two files into a third file
Open file1.txt and file2.txt in read mode then open file3.txt in write mode. Read the data from file1 and add it in a string. Read the data from file2 and concatenate the data of this file to the previous string then write the data from the string to file3 and close all the files
Python data = data2 = ""; # Reading data from file1 with open('file1.txt') as fp: data = fp.read() # Reading data from file2 with open('file2.txt') as fp: data2 = fp.read() # Merging 2 files # To add the data of file2 # from next line data += "\n" data += data2 with open ('file3.txt', 'w') as fp: fp.write(data) Output: 
Program to merge two files into a third file using a for loop
The above approach can be shortened using for loop. Create a list containing filenames then open file 3 in write mode. Iterate through the list and open each file in read mode. Read the data from files and simultaneously write the data in file3 and close all the files.
Python # Creating a list of filenames filenames = ['file1.txt', 'file2.txt'] # Open file3 in write mode with open('file3.txt', 'w') as outfile: # Iterate through list for names in filenames: # Open each file in read mode with open(names) as infile: # read the data from file1 and # file2 and write it in file3 outfile.write(infile.read()) # Add '\n' to enter data of file2 # from next line outfile.write("\n") Output:
Program to merge two files into a third file using the Shutil module
In this method, we use the shutil.copyfileobj() function to copy the contents of file1.txt and file2.txt into the merged_file.txt. The function shutil.copyfileobj() efficiently copies data from one file object to another, which is useful for merging files without loading the entire contents into memory at once.
Python import shutil def merge_files_with_shutil(file1, file2, merged_file): with open(merged_file, 'wb') as outfile: for filename in [file1, file2]: with open(filename, 'rb') as infile: shutil.copyfileobj(infile, outfile) # Usage: file1 = 'file1.txt' file2 = 'file2.txt' merged_file = 'merged_file.txt' merge_files_with_shutil(file1, file2, merged_file)
Output:
Program to merge two files into a third file using os module
The os module alone is not sufficient to merge files. We'll need to use file handles to read and write data. Here's the correct way to merge two files into a third file using the os module and file handles
Python import os def merge_files_with_os(file1, file2, merged_file): with open(merged_file, 'w') as outfile: for filename in [file1, file2]: with open(filename, 'r') as infile: for line in infile: outfile.write(line) # Usage: file1 = 'file1.txt' file2 = 'file2.txt' merged_file = 'merged_file.txt' merge_files_with_os(file1, file2, merged_file)
Output:
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