import difflib
a='abcd'
b='ab123'
seq=difflib.SequenceMatcher(a=a.lower(),b=b.lower())
seq=difflib.SequenceMatcher(a,b)
d=seq.ratio()*100
print d
I used the above code but obtained output is 0.0. How can I get a valid answer?
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docs.python.org/3/library/difflib.html#sequencematcher-objectsMartin Thoma– Martin Thoma2017-07-19 12:57:23 +00:00Commented Jul 19, 2017 at 12:57
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2 Answers
You forgot the first parameter to SequenceMatcher.
>>> import difflib
>>>
>>> a='abcd'
>>> b='ab123'
>>> seq=difflib.SequenceMatcher(None, a,b)
>>> d=seq.ratio()*100
>>> print d
44.4444444444
6 Comments
Mohsin
Hey nice answer, is there any way to get the number of matches?
Lennart Regebro
get_matching_blocks()
Mohsin
ya i got the all the strings, but it fails to find all the common strings even if you have autojunk set to false
Lennart Regebro
get_matching_blocks() literally will return a list of matching blocks. Hence, by doing len() on that list, you get the number of matches. Isn't that what you wanted? It's what you asked for.
Mohsin
Ya but the algorithm fails for longer length strings
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From the docs:
The SequenceMatcher class has this constructor:
class difflib.SequenceMatcher(isjunk=None, a='', b='', autojunk=True)
The problem in your code is that by doing
seq=difflib.SequenceMatcher(a,b)
you are passing a as value for isjunk and b as value for a, leaving the default '' value for b. This results in a ratio of 0.0.
One way to overcome this (already mentioned by Lennart) is to explicitly pass None as extra first parameter so all the keyword arguments get assigned the correct values.
However I just found, and wanted to mention another solution, that doesn't touch the isjunk argument but uses the set_seqs() method to specify the different sequences.
>>> import difflib
>>> a = 'abcd'
>>> b = 'ab123'
>>> seq = difflib.SequenceMatcher()
>>> seq.set_seqs(a.lower(), b.lower())
>>> d = seq.ratio()*100
>>> print d
44.44444444444444