String similarity metrics in Python


Question

I want to find string similarity between two strings. This page has examples of some of them. Python has an implemnetation of Levenshtein algorithm. Is there a better algorithm, (and hopefully a python library), under these contraints.

  1. I want to do fuzzy matches between strings. eg matches('Hello, All you people', 'hello, all You peopl') should return True
  2. False negatives are acceptable, False positives, except in extremely rare cases are not.
  3. This is done in a non realtime setting, so speed is not (much) of concern.
  4. [Edit] I am comparing multi word strings.

Would something other than Levenshtein distance(or Levenshtein ratio) be a better algorithm for my case?

1
42
7/2/2011 4:38:56 AM

Accepted Answer

There's a great resource for string similarity metrics at the University of Sheffield. It has a list of various metrics (beyond just Levenshtein) and has open-source implementations of them. Looks like many of them should be easy to adapt into Python.

http://web.archive.org/web/20081224234350/http://www.dcs.shef.ac.uk/~sam/stringmetrics.html

Here's a bit of the list:

  • Hamming distance
  • Levenshtein distance
  • Needleman-Wunch distance or Sellers Algorithm
  • and many more...
20
2/16/2016 1:45:46 PM

I realize it's not the same thing, but this is close enough:

>>> import difflib
>>> a = 'Hello, All you people'
>>> b = 'hello, all You peopl'
>>> seq=difflib.SequenceMatcher(a=a.lower(), b=b.lower())
>>> seq.ratio()
0.97560975609756095

You can make this as a function

def similar(seq1, seq2):
    return difflib.SequenceMatcher(a=seq1.lower(), b=seq2.lower()).ratio() > 0.9

>>> similar(a, b)
True
>>> similar('Hello, world', 'Hi, world')
False

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