Add ratio_min() function to the difflib library #90244

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1. gi-ba-bu commented on Dec 15, 2021

   

   gi-ba-bumannequin

   on Dec 15, 2021

   MannequinAuthor

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   Here I propose a new function, namely .ratio_min(self,m).

   .ratio_min(self,m) is an extension of the difflib's function .ratio(self). Equivalently to .ratio(self), .ratio_min(self,m) returns a measure of two sequences' similarity (float in [0,1]). In addition to .ratio(), it can ignore matched substrings if these substrings have length less than a given threshold m. m is the second variable of the function.

   It is very useful to avoid spurious high similarity scores.

   # NEW FUNCTION: 
   

       def ratio_min(self,m):
           """Return a measure of the sequences' similarity (float in [0,1]).
           Where T is the total number of elements in both sequences, and
           M_min is the number of matches with every single match has length at least m, this is 2.0*M_min / T.
           Note that this is 1 if the sequences are identical, and 0 if
           they have no substring of length m or more in common.
           .ratio_min() is similar to .ratio(). 
           .ratio_min(1) is equivalent to .ratio().
           
           >>> s = SequenceMatcher(None, "abcd", "bcde")
           >>> s.ratio_min(1)
           0.75
           >>> s.ratio_min(2)
           0.75
           >>> s.ratio_min(3)
           0.75
           >>> s.ratio_min(4)
           0.0
           """
   
           matches = sum(triple[-1] for triple in self.get_matching_blocks() if triple[-1] >=m)
           return _calculate_ratio(matches, len(self.a) + len(self.b))
2. gi-ba-bu

   added

   3.10 (EOL)end of lifeend of life

   3.11only security fixesonly security fixes

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-featureA feature request or enhancementA feature request or enhancement

   on Dec 15, 2021
3. AlexWaygood commented on Dec 15, 2021

   

   AlexWaygood

   on Dec 15, 2021

   Member

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   I am removing 3.10 from the "versions" field, since additions to the standard library are only considered for unreleased versions of Python.
4. AlexWaygood

   removed

   3.10 (EOL)end of lifeend of life

   on Dec 15, 2021
5. rhettinger

   assigned

   tim-one

   on Dec 15, 2021
6. taleinat commented on Jan 8, 2022

   

   taleinat

   on Jan 8, 2022

   Contributor

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   Thanks for the suggestion and the PR, Giacomo!

   However, in my opinion, this is better suited to be something like a cookbook recipe. The number of use cases for this will be low, and there would be little advantage to having this in the stdlib rather than elsewhere.
7. taleinat commented on Jan 20, 2022

   

   taleinat

   on Jan 20, 2022

   Contributor

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   I'm closing this for now since nobody has followed up and to the best of my understanding this wouldn't be an appropriate addition to the stdlib.

   This can be re-opened in the future if needed, of course.
8. taleinat

   closed this as completedon Jan 20, 2022
9. taleinat

   closed this as completedon Jan 20, 2022
10. ezio-melotti

    transferred this issue fromon Apr 10, 2022