[issue24384] difflib.SequenceMatcher faster quick_ratio with lower bound specification

[floyd]

floyd  added the comment:

Yes, I agree this should be closed. Especially because my proposed code is so 
incredibly bad (e.g. regarding performance) that it should be rejected. Back 
then I was horribly wrong and didn't understand the problem well enough yet.

If somebody would like to have such a function, this is all it needs:

def quick_ratio_ge(self, a, b, threshold):
return threshold <= 2.0*(len(a))/(len(a)+len(b))

Here is how I actually use it in code: 
https://github.com/modzero/burp-ResponseClusterer/blob/master/ResponseClusterer.py#L343

Sorry for the fuzz

--
resolution:  -> rejected
stage:  -> resolved
status: open -> closed

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[issue24384] difflib.SequenceMatcher faster quick_ratio with lower bound specification

[floyd]

New submission from floyd:

I guess a lot of users of difflib call the SequenceMatcher in the following way 
(where a and b often have different lengths):

if difflib.SequenceMatcher.quick_ratio(None, a, b) >= threshold:

However, for this use case the current quick_ratio is quite a performance loss. 
Therefore I propose to add an additional, optimized version quick_ratio_ge 
which would be called like this:

if difflib.SequenceMatcher.quick_ratio_ge(None, a, b, threshold):

As we are able to calculate upper bounds for threshold depending on the lengths 
of a and b this function would return much faster in a lot of cases.

An example of how quick_ratio_ge could be implemented is attached.

--
components: Library (Lib)
files: difflib_SequenceMatcher_quick_ratio_ge.py
messages: 244840
nosy: floyd
priority: normal
severity: normal
status: open
title: difflib.SequenceMatcher faster quick_ratio with lower bound specification
type: enhancement
Added file: 
http://bugs.python.org/file39625/difflib_SequenceMatcher_quick_ratio_ge.py

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[issue24384] difflib.SequenceMatcher faster quick_ratio with lower bound specification

[floyd]

floyd added the comment:

Now that I gave it another thought, I think it would be better if we simply add 
threshold as a named parameter of quick_ratio

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[issue24384] difflib.SequenceMatcher faster quick_ratio with lower bound specification

[floyd]

floyd added the comment:

Agree with the separate function (especially as the return value would change 
from float to bool).

In my experience this is one of the most often occuring use cases for difflib 
in practice.

Another reason is that it is not obvious that the user can optimize it with the 
appended version.

Some more opinions would be nice.

If this suggestion is rejected we could include a performance warning for this 
use case in the docs and/or I'll write an online code recipe which can be 
linked to.

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[issue5849] Idle 3.01 - invalid syntec error

[R.D. floyd]

New submission from R.D. floyd :

Recently upgraded to OS 10.5, Experienced Fortran, Basic, et. al.
programmer learning Python. IDLE 3.01 give invalid syntec error when
running program below. IDLE from MacPython 2.xx runs it ok!

--
components: IDLE
files: odbchelper.py
messages: 86609
nosy: r2d2floyd
severity: normal
status: open
title: Idle 3.01 - invalid syntec error
type: compile error
versions: Python 3.0
Added file: http://bugs.python.org/file13793/odbchelper.py

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