This is a simple python script to compare two text files line by line and output only the lines that are different.
Program Analysis
The program asks the user to input the names of the two files to compare. It will then open the files in read only mode and reads one line at a time from each file and compares them after stripping off any trailing whitespaces, which means we are ignoring new-line and spaces at the end of the line.
If the lines are different then it is printed out along with the corresponding line number and the prefix '>' or '<' to indicate the file.
An additional check is also carried out to determine if that specific line exist only on one file in which case it is indicated with a + sign in the output.
Program Source
# Ask the user to enter the names of files to compare fname1 = input("Enter the first filename: ") fname2 = input("Enter the second filename: ") # Open file for reading in text mode (default mode) f1 = open(fname1) f2 = open(fname2) # Print confirmation print("-----------------------------------") print("Comparing files ", " > " + fname1, " < " +fname2, sep='\n') print("-----------------------------------") # Read the first line from the files f1_line = f1.readline() f2_line = f2.readline() # Initialize counter for line number line_no = 1 # Loop if either file1 or file2 has not reached EOF while f1_line != '' or f2_line != '': # Strip the leading whitespaces f1_line = f1_line.rstrip() f2_line = f2_line.rstrip() # Compare the lines from both file if f1_line != f2_line: # If a line does not exist on file2 then mark the output with + sign if f2_line == '' and f1_line != '': print(">+", "Line-%d" % line_no, f1_line) # otherwise output the line on file1 and mark it with > sign elif f1_line != '': print(">", "Line-%d" % line_no, f1_line) # If a line does not exist on file1 then mark the output with + sign if f1_line == '' and f2_line != '': print("<+", "Line-%d" % line_no, f2_line) # otherwise output the line on file2 and mark it with < sign elif f2_line != '': print("<", "Line-%d" % line_no, f2_line) # Print a blank line print() #Read the next line from the file f1_line = f1.readline() f2_line = f2.readline() #Increment line counter line_no += 1 # Close the files f1.close() f2.close()
Program Output
Consider two text files file1.txt and file2.txt with the following contents
file1.txt
opentechguides website contains tutorials and howto articles on topics such as Linux Windows, databases etc.,
file2.txt
opentechguides website contains tutorials and howto articles on topics such as Linux Windows, databases , networking programming and web development.
If you compare these two files using our python script, the output will be as shown below:
Enter the first filename: file1.txt Enter the second filename: file2.txt ----------------------------------- Comparing files > file1.txt < file2.txt ----------------------------------- > Line-4 Windows, databases etc., < Line-4 Windows, databases , networking <+ Line-5 programming and web development.
