Python difflib, get offsets

Question

Is there a way in python with difflib to get offsets of the changes as well as the changes themselves?

What I have is the following:

import difflib

text1 = 'this is a sample text'.split()
text2 = 'this is text two.'.split()

print list(difflib.ndiff(text1, text2))

which prints:

['  this', '  is', '- a', '- sample', '  text', '+ two.']

Can I also get offsets of the corresponding changes? Naive solution would be just to search for changes, but if strings get longer with repeated terms, that wouldn't work.

Answer 1

SequenceMatcher.get_matching_blocks() might help. It returns a list of triples describing matching subsequences. These indices in turn could be used to find the location of differences.

>>> for block in s.get_matching_blocks():
...     print "a[%d] and b[%d] match for %d elements" % block
a[0] and b[0] match for 8 elements
a[8] and b[17] match for 21 elements
a[29] and b[38] match for 0 elements

https://docs.python.org/2/library/difflib.html#difflib.SequenceMatcher.get_matching_blocks https://docs.python.org/2/library/difflib.html#sequencematcher-examples