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bpo-46086: Add ratio_min(self,m) function - #30125

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bpo-46086: Add ratio_min(self,m) function#30125
gi-ba-bu wants to merge 1 commit into
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@gi-ba-bu

@gi-ba-bu gi-ba-bu commented Dec 15, 2021 •
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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 CODE:

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))

https://bugs.python.org/issue46086

@gi-ba-bu
Add ratio_min(self,m) function
c1a2e13 
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.
@the-knights-who-say-ni

the-knights-who-say-ni commented Dec 15, 2021

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Hello, and thanks for your contribution!

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Thanks again for the contribution, we look forward to reviewing it!

@AlexWaygood AlexWaygood mentioned this pull request Dec 15, 2021
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@taleinat

taleinat commented Jan 8, 2022 •
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I've added the "DO-NOT-MERGE" label for now, since this suggestion still requires discussion and acceptance.

Also, note that (if accepted) this change will need to be made only on the main branch, so this PR will need to be changed accordingly or replaced by a new PR.

@taleinat

taleinat commented Jan 20, 2022

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I'm closing this for now since nobody has followed up(here or on the issue tracker) 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.

@taleinat taleinat closed this Jan 20, 2022
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@gi-ba-bu @the-knights-who-say-ni @taleinat @bedevere-bot