code: def url(self, endpoint):
      
      return self.api_url.format(version=self.api_version,
                                 endpoint=self.api_endpoints[endpoint])
docs: Returns full URL for specified API endpoint
      >>> translate = YandexTranslate("trnsl.1.1.20130421T140201Z.323e508a33e9d84b.f1e0d9ca9bcd0a00b0ef71d82e6cf4158183d09e")
      >>> translate.url("langs")
      'https://translate.yandex.net/api/v1.5/tr.json/getLangs'
      >>> translate.url("detect")
      'https://translate.yandex.net/api/v1.5/tr.json/detect'
      >>> translate.url("translate")
      'https://translate.yandex.net/api/v1.5/tr.json/translate'