Compare Two Files for Differences in Python

Compare two files report difference in python

import difflib

lines1 = '''
dog
cat
bird
buffalo
gophers
hound
horse
'''.strip().splitlines()

lines2 = '''
cat
dog
bird
buffalo
gopher
horse
mouse
'''.strip().splitlines()

# Changes:
# swapped positions of cat and dog
# changed gophers to gopher
# removed hound
# added mouse

for line in difflib.unified_diff(lines1, lines2, fromfile='file1', tofile='file2', lineterm=''):
    print line

Outputs the following:

--- file1
+++ file2
@@ -1,7 +1,7 @@
+cat
 dog
-cat
 bird
 buffalo
-gophers
-hound
+gopher
 horse
+mouse

This diff gives you context -- surrounding lines to help make it clear how the file is different. You can see "cat" here twice, because it was removed from below "dog" and added above it.

You can use n=0 to remove the context.

for line in difflib.unified_diff(lines1, lines2, fromfile='file1', tofile='file2', lineterm='', n=0):
    print line

Outputting this:

--- file1
+++ file2
@@ -0,0 +1 @@
+cat
@@ -2 +2,0 @@
-cat
@@ -5,2 +5 @@
-gophers
-hound
+gopher
@@ -7,0 +7 @@
+mouse

But now it's full of the "@@" lines telling you the position in the file that has changed. Let's remove the extra lines to make it more readable.

for line in difflib.unified_diff(lines1, lines2, fromfile='file1', tofile='file2', lineterm='', n=0):
    for prefix in ('---', '+++', '@@'):
        if line.startswith(prefix):
            break
    else:
        print line

Giving us this output:

+cat
-cat
-gophers
-hound
+gopher
+mouse

Now what do you want it to do?
If you ignore all removed lines, then you won't see that "hound" was removed.
If you're happy just showing the additions to the file, then you could do this:

diff = difflib.unified_diff(lines1, lines2, fromfile='file1', tofile='file2', lineterm='', n=0)
lines = list(diff)[2:]
added = [line[1:] for line in lines if line[0] == '+']
removed = [line[1:] for line in lines if line[0] == '-']

print 'additions:'
for line in added:
    print line
print
print 'additions, ignoring position'
for line in added:
    if line not in removed:
        print line

Outputting:

additions:
cat
gopher
mouse

additions, ignoring position:
gopher
mouse

You can probably tell by now that there are various ways to "print the differences" of two files, so you will need to be very specific if you want more help.

Compare two different files line by line in python

This solution reads both files in one pass, excludes blank lines, and prints common lines regardless of their position in the file:

with open('some_file_1.txt', 'r') as file1:
    with open('some_file_2.txt', 'r') as file2:
        same = set(file1).intersection(file2)

same.discard('\n')

with open('some_output_file.txt', 'w') as file_out:
    for line in same:
        file_out.write(line)

Python - Compare 2 files and output differences

This is working for me:

def compare(File1,File2):
    with open(File1,'r') as f:
        d=set(f.readlines())

    with open(File2,'r') as f:
        e=set(f.readlines())

    open('file3.txt','w').close() #Create the file

    with open('file3.txt','a') as f:
        for line in list(d-e):
           f.write(line)

You need to compare the readlines set and find out lines that are not present in file2. You can then append these lines to the new file.

Compare two files and remove the common lines

Read the lines of both files into a separate variables. Iterate over the lines of the first file, and for each of one them check if they exist on the second file, if not then save them into the first file.

with open(file1, "r") as file1:
     lines_file1 = file1.readlines()
with open(file, "r") as file2:
     lines_file2 = file2.readlines()
     with open(file1, "w") as f_w:
           for line in lines_file1:
               if line not in lines_file2
                  f_w.write(line)

The downside of this approach is that you are loading the entire files into memory.

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