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Re: Don't understand SequenceMatcher from difflib

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  Re: Don't understand SequenceMatcher from difflib Terry Reedy <tjreedy@udel.edu> - 2011-06-21 15:02 -0400

#8114 — Re: Don't understand SequenceMatcher from difflib

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

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