Python "regex" module: Fuzziness value

Question

I'm using the "fuzzy match" functionality of the Regex module.

How can I get the "fuzziness value" of a "match" which indicates how different the pattern is to the string, just like the "edit distance" in Levenshtein?

I thought I could get the value in the Match object, but it's not there. The official docs said nothing about it, neither.

e.g.:

regex.match('(?:foo){e}','for')

a.captures() tells me that the word "for" is matched, but I'd like to know the fuzziness value, which should be 1 in this case.

Is there any way to achieve that?

It's certainly not ideal, but if all else fails you could try repeated attempts with (?:foo){e<=i} where you loop over some integer i. The first time you get a match, your i is the Levenshtein distance. — Martin Ender
– Martin Ender, Commented Jun 10, 2013 at 12:53
Or if you are working with a limited number of errors you could use something like (foo)|((?:foo){e=1})|((?:foo){e=2}) and check which group matched, if first e = 0, second e = 1, etc. — Qtax
– Qtax, Commented Jun 10, 2013 at 13:10

falsetru · Accepted Answer · 2013-06-10 13:05:22Z

2

>>> import difflib
>>> matcher = difflib.SequenceMatcher(None, 'foo', 'for')
>>> sum(size for start, end, size in matcher.get_matching_blocks())
2
>>> max(map(len, ('foo', 'for'))) - _
1
>>>
>>>
>>> matcher = difflib.SequenceMatcher(None, 'foo', 'food')
>>> sum(size for start, end, size in matcher.get_matching_blocks())
3
>>> max(map(len, ('foo', 'food'))) - _
1

http://docs.python.org/2/library/difflib.html#difflib.SequenceMatcher.get_matching_blocks http://docs.python.org/2/library/difflib.html#difflib.SequenceMatcher.get_opcodes

answered Jun 10, 2013 at 13:05

falsetru

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3 Comments

tslmy Over a year ago

Errrr... This workaround is great, and difflib is good stuff, too. But I have to use the "groupdict" thing in re/regex, so, I don't think difflib is suitable for that. Thanks all the same.

tslmy Over a year ago

I replaced the regex module with the difflib like you said, and it works like a charm! So, I wonder is this "SequenceMatcher" thing comparable to the Levenshtein algrithm?

falsetru Over a year ago

In source code, there is no mention about Levenshtein. (I didn't read throughly.)

Community · Accepted Answer · 2017-05-23 12:32:39Z

0

a = regex.match('(?:foo){e}','for')
a.fuzzy_counts

this returns a tuple (x,y,z) where:

x = number of substitutions

y = number of insertions and

z = number of deletions

But this is not always a reliable count, ie: the regex match fuzziness night not equate to the true Levinstein distance in some cases

Python regex module fuzzy match: substitution count not as expected

edited May 23, 2017 at 12:32

CommunityBot

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answered Jul 8, 2016 at 15:07

Colin Anthony

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