def add_default_language_settings(languages_list, var_name='PARLER_LANGUAGES', **extra_defaults):
    """
    Apply extra defaults to the language settings.
    This function can also be used by other packages to
    create their own variation of ``PARLER_LANGUAGES`` with extra fields.
    For example::

        from django.conf import settings
        from parler import appsettings as parler_appsettings

        # Create local names, which are based on the global parler settings
        MYAPP_DEFAULT_LANGUAGE_CODE = getattr(settings, 'MYAPP_DEFAULT_LANGUAGE_CODE', parler_appsettings.PARLER_DEFAULT_LANGUAGE_CODE)
        MYAPP_LANGUAGES = getattr(settings, 'MYAPP_LANGUAGES', parler_appsettings.PARLER_LANGUAGES)

        # Apply the defaults to the languages
        MYAPP_LANGUAGES = parler_appsettings.add_default_language_settings(MYAPP_LANGUAGES, 'MYAPP_LANGUAGES',
            code=MYAPP_DEFAULT_LANGUAGE_CODE,
            fallback=MYAPP_DEFAULT_LANGUAGE_CODE,
            hide_untranslated=False
        )

    The returned object will be an :class:`~parler.utils.conf.LanguagesSetting` object,
    which adds additional methods to the :class:`dict` object.

    :param languages_list: The settings, in :ref:`PARLER_LANGUAGES` format.
    :param var_name: The name of your variable, for debugging output.
    :param extra_defaults: Any defaults to override in the ``languages_list['default']`` section, e.g. ``code``, ``fallback``, ``hide_untranslated``.
    :return: The updated ``languages_list`` with all defaults applied to all sections.
    :rtype: LanguagesSetting
    """
    languages_list = LanguagesSetting(languages_list)

    languages_list.setdefault('default', {})
    defaults = languages_list['default']
    defaults.setdefault('hide_untranslated', False)   # Whether queries with .active_translations() may or may not return the fallback language.

    if 'fallback' in defaults:
        #warnings.warn("Please use 'fallbacks' instead of 'fallback' in the 'defaults' section of {0}".format(var_name), DeprecationWarning)
        defaults['fallbacks'] = [defaults.pop('fallback')]
    if 'fallback' in extra_defaults:
        #warnings.warn("Please use 'fallbacks' instead of 'fallback' in parameters for {0} = add_default_language_settings(..)".format(var_name), DeprecationWarning)
        extra_defaults['fallbacks'] = [extra_defaults.pop('fallback')]

    defaults.update(extra_defaults)  # Also allow to override code and fallback this way.

    # This function previously existed in appsettings, where it could reference the defaults directly.
    # However, this module is a more logical place for this function. To avoid circular import problems,
    # the 'code' and 'fallback' parameters are always passed by the appsettings module.
    # In case these are missing, default to the original behavior for backwards compatibility.
    if 'code' == defaults:
        from parler import appsettings
        defaults['code'] = appsettings.PARLER_DEFAULT_LANGUAGE_CODE
    if 'fallbacks' not in defaults:
        from parler import appsettings
        defaults['fallbacks'] = [appsettings.PARLER_DEFAULT_LANGUAGE_CODE]

    if not is_supported_django_language(defaults['code']):
        raise ImproperlyConfigured("The value for {0}['defaults']['code'] ('{1}') does not exist in LANGUAGES".format(var_name, defaults['code']))

    for site_id, lang_choices in six.iteritems(languages_list):
        if site_id == 'default':
            continue

        if not isinstance(lang_choices, (list, tuple)):
            raise ImproperlyConfigured("{0}[{1}] should be a tuple of language choices!".format(var_name, site_id))
        for i, choice in enumerate(lang_choices):
            if not is_supported_django_language(choice['code']):
                raise ImproperlyConfigured("{0}[{1}][{2}]['code'] does not exist in LANGUAGES".format(var_name, site_id, i))

            # Copy all items from the defaults, so you can provide new fields too.
            for key, value in six.iteritems(defaults):
                choice.setdefault(key, value)

    return languages_list
dataset/ETHPy150Open edoburu/django-parler/parler/utils/conf.py/add_default_language_settings/operator `not in` -> `==`