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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Don't understand SequenceMatcher from difflib
Date: Tue, 21 Jun 2011 15:02:57 -0400
References: <20110621134305.GA8929@trout.vub.ac.be>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:8114

On 6/21/2011 9:43 AM, Antoon Pardon wrote:

>    matcher = SequenceMatcher(ls1, ls2)
...
> What am I doing wrong?

Read the doc, in particular, the really stupid signature of the class:

"class difflib.SequenceMatcher(isjunk=None, a='', b='', autojunk=True)"
You are passing isjunk = ls1, a = ls2, and by default, b=''. So there 
are no matches, len(a) = 36, len(b) = 0, and the dummy match is (36,0,0) 
as you got.

There are also several example in the doc, all like
 >>> s = SequenceMatcher(None, " abcd", "abcd abcd") # or
 >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd")

So you will get better results with
matcher = SequenceMatcher(None, ls1, ls2) # or
matcher = SequenceMatcher(a=ls1, b=ls2)

In the future, please try to simply examples before posting for help.

print(list(SequenceMatcher('a','abc').get_matching_blocks()))

shows the problem you posted in one easily read line of input and 
output. I only waded through the distracting code and output you posted 
to find that problem because I patched SequenceMatcher last fall.

-- 
Terry Jan Reedy