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[mod] add locale.get_engine_locale to get predictable results

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The match_language function sometimes returns incorrect results which is why a
new function get_engine_locale is required.

A bugfix of the match_language is not easily possible, because there is almost
no documentation for it and already the call parameters are undefined.  E.g. the
function processes values like the ones from yahoo::

    "yahoo": [
        "ar",
        ...
        "zh_chs",
        "zh_cht"
     ]

The get_engine_locale has been documented in detail, there is a clear
description of the assumptions as well as the requirements and approximation
rules (read doc-string for more details)::

    Argument ``engine_locales`` is a python dict that maps *SearXNG locales* to
    corresponding *engine locales*:

      <engine>: {
          # SearXNG string : engine-string
          'ca-ES'          : 'ca_ES',
          'fr-BE'          : 'fr_BE',
          'fr-CA'          : 'fr_CA',
          'fr-CH'          : 'fr_CH',
          'fr'             : 'fr_FR',
          ...
          'pl-PL'          : 'pl_PL',
          'pt-PT'          : 'pt_PT'
      }

    .. hint::

       The *SearXNG locale* string has to be known by babel!

In the following you will find a comparison:

>>> import babel.languages
>>> from searx.utils import match_language
>>> from searx.locales import get_engine_locale

Assume we have an engine that supports the follwoing locales:

>>> lang_list = {
...     "zh-CN": "zh_CN",
...     "zh-HK": "zh_HK",
...     "nl-BE": "nl_BE",
...     "fr-CA": "fr_CA",
... }

Assumption:

  A. When a user selects a language the results should be optimized according to
     the selected language.

  B. When user selects a language and a territory the results should be
     optimized with first priority on territory and second on language.

----

Example: (Assumption A.)

  A user selects region 'zh-TW' which should end in zh_HK

hint:
  CN is 'Hans' and HK ('Hant') fits better to TW ('Hant')

>>> get_engine_locale('zh-TW', lang_list)
'zh_HK'
>>> lang_list[match_language('zh-TW', lang_list)]
'zh_CN'

----

Example: (Assumption A.)

  A user selects only the language 'zh' which should end in CN

>>> get_engine_locale('zh', lang_list)
'zh_CN'
>>> lang_list[match_language('zh', lang_list)]
'zh_CN'

----

Example: (Assumption B.)

  A user selects region 'fr-BE' which should end in nl-BE

hint:
  priority should be on the territory the user selected.  If the user
  prefers 'fr' he will select 'fr' without a region tag.

>>> get_engine_locale('fr-BE', lang_list, default='unknown')
'nl_BE'
>>> match_language('fr-BE', lang_list, fallback='unknown')
'fr-CA'

----

Example: (Assumption A.)

  A user selects only the language 'fr' which should end in fr_CA

>>> get_engine_locale('fr', lang_list)
'fr_CA'
>>> lang_list[match_language('fr', lang_list)]
'fr_CA'

----

The difference in priority on the territory is best shown with a engine that
supports the following locales:

>>> lang_list = {
...     "fr-FR": "fr_FR",
...     "fr-CA": "fr_CA",
...     "en-GB": "en_GB",
...     "nl-BE": "nl_BE",
... }

----

Example: (Assumption A.)

   A user selects only a language

>>> get_engine_locale('en', lang_list)
'en_GB'
>>> match_language('en', lang_list)
'en-GB'

hint: the engine supports fr_FR and fr_CA since no territory is given, fr_FR
takes priority ..

>>> get_engine_locale('fr', lang_list)
'fr_FR'
>>> lang_list[match_language('fr', lang_list)]
'fr_FR'

----

Example: (Assumption B.)

  A user selects region 'fr-BE' which should end in nl-BE

>>> get_engine_locale('fr-BE', lang_list)
'nl_BE'
>>> lang_list[match_language('fr-BE', lang_list)]
'fr_FR'

----

If the user selects a language and there are two locales like the following:

>>> lang_list = {
...      "fr-BE": "fr_BE",
...      "fr-CH": "fr_CH",
...  }
>>>

>>> get_engine_locale('fr', lang_list)
'fr_BE'
>>> lang_list[match_language('fr', lang_list)]
'fr_BE'

Looks like both functions return the same value, but match_language depends on the
order of the dictionary (which is not predictable):

>>> lang_list = {
...      "fr-CH": "fr_CH",
...      "fr-BE": "fr_BE",
...  }
>>> get_engine_locale('fr', lang_list)
'fr_BE'
>>> lang_list[match_language('fr', lang_list)]
'fr_CH'
>>>

The get_engine_locale selects the locale by looking at the "population percent"
and this percentage has an higher amount in BE (68.%) compared to CH (21%)

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
This commit is contained in:
Markus Heiser 2022-08-12 17:46:20 +02:00
parent 75bb8c45d0
commit 9ae409a05a
1 changed files with 137 additions and 0 deletions
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137
searx/locales.py
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@ -10,6 +10,8 @@ import pathlib
from babel import Locale
from babel.support import Translations
import babel.languages
import babel.core
import flask_babel
import flask
from flask.ctx import has_request_context
@ -150,3 +152,138 @@ def locales_initialize(directory=None):
LOCALE_NAMES[tag] = get_locale_descr(locale, dirname)
if locale.text_direction == 'rtl':
RTL_LOCALES.add(tag)
def get_engine_locale(searxng_locale, engine_locales, default=None):
"""Return engine's language (aka locale) string that best fits to argument
``searxng_locale``.
Argument ``engine_locales`` is a python dict that maps *SearXNG locales* to
corresponding *engine locales*:
<engine>: {
# SearXNG string : engine-string
'ca-ES' : 'ca_ES',
'fr-BE' : 'fr_BE',
'fr-CA' : 'fr_CA',
'fr-CH' : 'fr_CH',
'fr' : 'fr_FR',
...
'pl-PL' : 'pl_PL',
'pt-PT' : 'pt_PT'
}
.. hint::
The *SearXNG locale* string has to be known by babel!
If there is no direct 1:1 mapping, this functions tries to narrow down
engine's language (locale). If no value can be determined by these
approximation attempts the ``default`` value is returned.
Assumptions:
A. When user select a language the results should be optimized according to
the selected language.
B. When user select a language and a territory the results should be
optimized with first priority on terrirtory and second on language.
First approximation rule (*by territory*):
When the user selects a locale with terrirtory (and a language), the
territory has priority over the language. If any of the offical languages
in the terrirtory is supported by the engine (``engine_locales``) it will
be used.
Second approximation rule (*by language*):
If "First approximation rule" brings no result or the user selects only a
language without a terrirtory. Check in which territories the language
has an offical status and if one of these territories is supported by the
engine.
"""
# pylint: disable=too-many-branches
engine_locale = engine_locales.get(searxng_locale)
if engine_locale is not None:
# There was a 1:1 mapping (e.g. "fr-BE --> fr_BE" or "fr --> fr_FR"), no
# need to narrow language nor territory.
return engine_locale
locale = babel.Locale.parse(searxng_locale, sep='-')
# SearXNG's selected locale is not supported by the engine ..
if locale.territory:
# Try to narrow by *offical* languages in the territory (??-XX).
for official_language in babel.languages.get_official_languages(locale.territory, de_facto=True):
searxng_locale = official_language + '-' + locale.territory
engine_locale = engine_locales.get(searxng_locale)
if engine_locale is not None:
return engine_locale
# Engine does not support one of the offical languages in the territory or
# there is only a language selected without a territory.
# Now lets have a look if the searxng_lang (the language selected by the
# user) is a offical language in other territories. If so, check if
# engine does support the searxng_lang in this other territory.
if locale.language:
searxng_lang = locale.language
if locale.script:
searxng_lang += '_' + locale.script
terr_lang_dict = {}
for territory, langs in babel.core.get_global("territory_languages").items():
if not langs.get(searxng_lang, {}).get('official_status'):
continue
terr_lang_dict[territory] = langs.get(searxng_lang)
# first: check fr-FR, de-DE .. is supported by the engine
territory = locale.language.upper()
if terr_lang_dict.get(territory):
searxng_locale = locale.language + '-' + territory
engine_locale = engine_locales.get(searxng_locale)
if engine_locale is not None:
return engine_locale
# second: sort by population_percent and take first match
# drawback of "population percent": if there is a terrirtory with a
# small number of people (e.g 100) but the majority speaks the
# language, then the percentage migth be 100% (--> 100 people) but in
# a different terrirtory with more people (e.g. 10.000) where only 10%
# speak the language the total amount of speaker is higher (--> 200
# people).
#
# By example: The population of Saint-Martin is 33.000, of which 100%
# speak French, but this is less than the 30% of the approximately 2.5
# million Belgian citizens
#
# - 'fr-MF', 'population_percent': 100.0, 'official_status': 'official'
# - 'fr-BE', 'population_percent': 38.0, 'official_status': 'official'
terr_lang_list = []
for k, v in terr_lang_dict.items():
terr_lang_list.append((k, v))
for territory, _lang in sorted(terr_lang_list, key=lambda item: item[1]['population_percent'], reverse=True):
searxng_locale = locale.language + '-' + territory
engine_locale = engine_locales.get(searxng_locale)
if engine_locale is not None:
return engine_locale
# No luck: narrow by "language from territory" and "territory from language"
# does not fit to a locale supported by the engine.
if engine_locale is None:
engine_locale = default
return default