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Question about SequenceMatcher.quick_ratio

INADA Naoki-2
Hi, all.

I am one of  translator of Python document.
But I am not good at English well.

I can't understand one sentence in:
http://docs.python.org/library/difflib.html#difflib.SequenceMatcher.quick_ratio

> This isn’t defined beyond that it is an upper bound on ratio(), and is faster to compute.

I see that quick_ratio() calculates upper bound of ratio().
But I can't get what "this isn't defined beyond that" means.
May someone explain this in easy sentence for me?

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Re: Question about SequenceMatcher.quick_ratio

Brandon Craig Rhodes
INADA Naoki <[hidden email]> writes:

> I am one of translator of Python document.  But I am not good at
> English well.  I can't understand one sentence ...
>
>> This isn’t defined beyond that it is an upper bound on ratio(), and
>> is faster to compute.

The word "bound" works like this: a "bound" or "boundary" means a limit
or edge, so often it gets used in math like this:

    "I am not sure what the exact value of 'pi' is, but I have done some
     work and established a lower bound of 3.0 and an upper bound of 3.2
     for its true value."

This means, more simply, that 'pi' lies "between 3.0 and 3.2", but math
people have the specific names "lower bound" and "upper bound" for the
limits that they work out for the value of an unknown or difficult-to-
compute number.

So when 'quick_ratio()' claims to return an "upper bound on ratio()", it
means that it returns a number that 'ratio()' is guaranteed to be "less
than"; it sets, in other words, an upper limit on what the actual value
of  'ratio()' might be.

So if 'quick_ratio()' returns 0.8, it means that 'ratio()' itself might
be 0.8, or 0.6, or 0.003, or 0.00062, or even 0; that is, it might be
any permissible ratio value (they run from 0 to 1) that is not more than
0.8 because 'quick_ratio()' has done some checking and is sure that the
actual 'ratio()' is less than or equal to 0.8.

So did my English make the docs any clearer?  Or am I just as confusing? :-)

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Brandon Craig Rhodes   [hidden email]   http://rhodesmill.org/brandon
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Re: Question about SequenceMatcher.quick_ratio

Doug Hellmann-3
In reply to this post by INADA Naoki-2

On May 6, 2010, at 10:48 AM, INADA Naoki wrote:

> Hi, all.
>
> I am one of  translator of Python document.
> But I am not good at English well.
>
> I can't understand one sentence in:
> http://docs.python.org/library/difflib.html#difflib.SequenceMatcher.quick_ratio
>
>> This isn’t defined beyond that it is an upper bound on ratio(), and  
>> is faster to compute.
>
> I see that quick_ratio() calculates upper bound of ratio().
> But I can't get what "this isn't defined beyond that" means.
> May someone explain this in easy sentence for me?

I think it means that the implementation of quick_ratio() is not  
defined in a lot of detail, except to say that the function will  
return a value that is an upper bound of the value returned by  
ratio().  So the value returned by ratio() will always be less than or  
equal to the value returned by quick_ratio(), and quick_ratio() is  
faster than ratio().  real_quick_ratio() has a similar relationship to  
quick_ratio().

Doug

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Re: Question about SequenceMatcher.quick_ratio

INADA Naoki-2
Thank you, Branodn and  Doug for quick reply!

The word "upper bound" is also used in Japan with mathematics.

> I think it means that the implementation of quick_ratio() is not defined in
> a lot of detail, except to say that the function will return a value that is
> an upper bound of the value returned by ratio().

That's the answer I wanted!!

I've got "This isn't defined beyond that" means
"This method is not defined in detail more than".

I've misread that "beyond" means "over the upper bound".
Maybe, "more" is easier than "beyond" for non-native English
readers.

Thank you very well.
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Re: Question about SequenceMatcher.quick_ratio

Doug Hellmann-3

On May 6, 2010, at 11:27 AM, INADA Naoki wrote:

> Thank you, Branodn and  Doug for quick reply!
>
> The word "upper bound" is also used in Japan with mathematics.
>
>> I think it means that the implementation of quick_ratio() is not  
>> defined in
>> a lot of detail, except to say that the function will return a  
>> value that is
>> an upper bound of the value returned by ratio().
>
> That's the answer I wanted!!
>
> I've got "This isn't defined beyond that" means
> "This method is not defined in detail more than".
>
> I've misread that "beyond" means "over the upper bound".
> Maybe, "more" is easier than "beyond" for non-native English
> readers.

I agree that the current English phrasing is confusing to non-native  
speakers.  You should open a ticket in the tracker and ask for that  
text to be clarified.

Doug

>
> Thank you very well.
> --
> INADA Naoki  <[hidden email]>
> _______________________________________________
> Doc-SIG maillist  -  [hidden email]
> http://mail.python.org/mailman/listinfo/doc-sig

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Re: Question about SequenceMatcher.quick_ratio

Nick Coghlan
Doug Hellmann wrote:

>> I've got "This isn't defined beyond that" means
>> "This method is not defined in detail more than".
>>
>> I've misread that "beyond" means "over the upper bound".
>> Maybe, "more" is easier than "beyond" for non-native English
>> readers.
>
> I agree that the current English phrasing is confusing to non-native
> speakers.  You should open a ticket in the tracker and ask for that text
> to be clarified.

Or, as Georg pointed out recently, email [hidden email] mentioning the
problem (tracker is best, but an email to the docs address is better
than not reporting it directly at all).

Cheers,
Nick.

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Re: Question about SequenceMatcher.quick_ratio

INADA Naoki-2
I've posted it as a bug 8686.
http://bugs.python.org/issue8686#

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