[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

Serhiy Storchaka added the comment:


New changeset f6595983e08fe20cf06a2535d74d912c6dbb044f by Serhiy Storchaka in 
branch 'master':
bpo-28692: Deprecate using non-integer value for selecting a plural form in 
gettext. (#507)
https://github.com/python/cpython/commit/f6595983e08fe20cf06a2535d74d912c6dbb044f


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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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pull_requests:  -605

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Larry Hastings]

Changes by Larry Hastings :


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pull_requests: +605

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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pull_requests: +416

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Julien Palard]

Julien Palard added the comment:

> It seems to me that a fractional number should be formatted with the same 
> form independently from it's value

Ok, so 1.000 seconds, ok, LGTM.

Should we mention something explicit about it? Not sure how to write it down, 
but I still fear that everyone's reaction will be "Oh can't give a float? Let 
my put a round() in my call" and stay with the same plural bug as before.

Maybe replace

> Plural value must be an integer

by

> Should not use ngettext with floating point, consider an invariant form.

?

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

round() was used because it is the simplest way to convert fractional numbers 
to integers that doesn't involve strings-to-integer converting (as in int()). 
Perhaps math.trunc() looks a little more appropriate. math.ceil() returns a 
float in 2.7 and is limited by float range. But "1.678 second" don't look more 
correct than "1.678 seconds". My point is that gettext ability of selecting 
plural form shouldn't be used for fractional numbers. It seems to me that a 
fractional number should be formatted with the same form independently from 
it's value (it can be different from plural forms for integer numbers). 
Proposed patch adds a deprecating warning for encouraging users to rewrite 
their code for formatting fractional numbers.

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Julien Palard]

Julien Palard added the comment:

> But gettext formulas are not purposed to support non-integer values and can 
> return incorrect result

Looks like the cast to integer is done *before* giving the value to the C 
gettext expression.

> For example (in Ukrainian)

As long as gettext expression don't support non-integer values, there exist 
*no* way to support two languages where plural form differ for non-integer 
value. Typically if a language A consider 1.5 to be singular and another 
language B consider 1.5 to be plural, the only place in the code that can make 
the difference IS in the C plural expression which don't support non-integer 
values.

Rouding the value before giving it to ngettext only fixes the issue for the 
lang of the current developer, as for other languages, translators won't be 
able to change the rounding properties.

But should we bet that in most, any, or all languages, 1.5 is considered 
plural? I think so, according to wikipedia¹: "Plural of nouns typically denote 
a quantity other than the default quantity represented by a noun, which is 
generally one."

So, I think that a better fix than warning for non-integer values may be to 
round them using math.ceil instead of round. This way we avoid developpers to 
drop round() everywhere to fix the warning the wrong way, leaving the same bug 
you're having in Ukrainian.

¹: https://en.wikipedia.org/wiki/Plural

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Xiang Zhang]

Xiang Zhang added the comment:

Ohh, sorry. It should be 4 and I make a mistake. Sorry for the noise. Patch 
LGTM.

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Xiang Zhang]

Xiang Zhang added the comment:

I think the stacklevel should be 3.

stacklevel = 3:

./python -Walways /tmp/a.py 
/tmp/a.py:2: DeprecationWarning: Plural value must be an integer, got float
  c2py('n!=1')(1.1)

stacklevel = 4:

./python -Walways /tmp/a.py 
sys:1: DeprecationWarning: Plural value must be an integer, got float

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Yes, of cause. Thank your for noticing this.

--
Added file: 
http://bugs.python.org/file45487/gettext-non-int-plural-deprecate.patch

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Xiang Zhang]

Xiang Zhang added the comment:

Maybe you have forgotten to remove the debug print in the patch?

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nosy: +xiang.zhang

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Sorry. Here is a patch.

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keywords: +patch
Added file: 
http://bugs.python.org/file45485/gettext-non-int-plural-deprecate.patch

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Julien Palard]

Julien Palard added the comment:

Hi, did you forget to attach the patch?

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nosy: +mdk

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[issue28692] gettext: deprecate selecting plural form by fractional numbers

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

GNU gettext library accepts only integer value for selecting plural form. 
Python gettext accepts arbitrary numbers. But gettext formulas are not purposed 
to support non-integer values and can return incorrect result. For example (in 
Ukrainian):

   "1 площа", but "1.5 площі", not "1.5 площ".
   "2 гектари", but "2.75 гектара", not "2.75 гектарів".
   "5 тонн", but "5.7 тонни", not "5.7 тонн".

Separate plural form should be used for fractional numbers. Even if fractional 
part happens to be zero, it is acceptable (e.g. "Time elapsed: 1.000 seconds" 
in English).

Proposed patch deprecates fractional numbers for selecting plural form in 
gettext.

--
components: Library (Lib)
messages: 280804
nosy: Tim.Graham, loewis, serhiy.storchaka
priority: normal
severity: normal
stage: patch review
status: open
title: gettext: deprecate selecting plural form by fractional numbers
type: enhancement
versions: Python 3.7

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