Comparing two .txt files using difflib in Python

Question

I am trying to compare two text files and output the first string in the comparison file that does not match but am having difficulty since I am very new to python. Can anybody please give me a sample way to use this module.

When I try something like:

result = difflib.SequenceMatcher(None, testFile, comparisonFile)

I get an error saying object of type 'file' has no len.

Answer 1

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 anyway. To get the first non-matching string, I'll direct you to the wonderful world of difflib documentation.

Answer 2

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), 

Answer 3

Are you sure both files exist ?

Just tested it and i get a perfect result.

To get the results i use something like:

import difflib

diff=difflib.ndiff(open(testFile).readlines(), open(comparisonFile).readlines())

try:
    while 1:
        print diff.next(),
except:
    pass

the first character of each line indicates if they are different: eg.: '+' means the following line has been added, etc.