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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_country_by_id(self, country_id) -> 'Country': """ Gets a country in this coalition by its ID Args: country_id: country Id Returns: Country """

        VALID_POSITIVE_INT.validate(country_id, 'get_country_by_id', exc=ValueError)
        if country_id not in self._countries_by_id.keys():
            for country in self.countries:

                if country.country_id == country_id:
                    return country
            raise ValueError(country_id)
        else:
            return self._countries_by_id[country_id]