Returning lines that differ between two files (Python)

Question

I have two files with tens of thousands of lines each, output1.txt and output2.txt. I want to iterate through both files and return the line (and content) of the lines that diff

Answer 1

As long as you don't care about order you could use:

with open('file1') as f:
    t1 = f.read().splitlines()
    t1s = set(t1)

with open('file2') as f:
    t2 = f.read().splitlines()
    t2s = set(t2)

#in file1 but not file2
print "Only in file1"
for diff in t1s-t2s:
    print t1.index(diff), diff

#in file2 but not file1
print "Only in file2"
for diff in t2s-t1s:
    print t2.index(diff), diff

Edit: If you do care about order and they're mostly the same then why not just use the command diff?