Comparing two .txt files using difflib in Python

For starters, you need to pass strings to difflib.SequenceMatcher, not files:

# Like so
difflib.SequenceMatcher(None, str1, str2)

# Or just read the files in
difflib.SequenceMatcher(None, file1.read(), file2.read())

That'll fix your error.

To get the first non-matching string, see the difflib documentation.

Here is a quick example of comparing the contents of two files using Python difflib...

import difflib

file1 = "myFile1.txt"
file2 = "myFile2.txt"

diff = difflib.ndiff(open(file1).readlines(),open(file2).readlines())
print ''.join(diff),