def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def ngettext(self, singular: str, plural: str, lang: str = None, n=1):
        """
        Plural translations
        """
        if lang is None:
            lang = self.context_lang.get()

        if lang not in self.translations:
            if n == 1:
                return singular
            return plural

        translator = self.translations[lang]
        return translator.ngettext(singular, plural, n)