Python difflib: highlighting differences inline?

Question

When comparing similar lines, I want to highlight the differences on the same line:

a) lorem ipsum dolor sit amet
b) lorem foo ipsum dolor amet

lorem <ins>foo</ins> ipsum dolor <del>sit</del> amet

While difflib.HtmlDiff appears to do this sort of inline highlighting, it produces very verbose markup.

Unfortunately, I have not been able to find another class/method which does not operate on a line-by-line basis.

Am I missing anything? Any pointers would be appreciated!

Answer 1

difflib.SequenceMatcher will operate on single lines. You can use the "opcodes" to determine how to change the first line to make it the second line.

Answer 2

For your simple example:

import difflib
def show_diff(seqm):
    """Unify operations between two compared strings
seqm is a difflib.SequenceMatcher instance whose a & b are strings"""
    output= []
    for opcode, a0, a1, b0, b1 in seqm.get_opcodes():
        if opcode == 'equal':
            output.append(seqm.a[a0:a1])
        elif opcode == 'insert':
            output.append("<ins>" + seqm.b[b0:b1] + "</ins>")
        elif opcode == 'delete':
            output.append("<del>" + seqm.a[a0:a1] + "</del>")
        elif opcode == 'replace':
            raise NotImplementedError, "what to do with 'replace' opcode?"
        else:
            raise RuntimeError, "unexpected opcode"
    return ''.join(output)

>>> sm= difflib.SequenceMatcher(None, "lorem ipsum dolor sit amet", "lorem foo ipsum dolor amet")
>>> show_diff(sm)
'lorem<ins> foo</ins> ipsum dolor <del>sit </del>amet'

This works with strings. You should decide what to do with "replace" opcodes.