def asset(self, asset_id, query=None):
        """Fetches an Asset by ID.

        API Reference: https://www.contentful.com/developers/docs/references/content-delivery-api/#/reference/assets/asset/get-a-single-asset

        :param asset_id: The ID of the target Asset.
        :param query: (optional) Dict with API options.
        :return: :class:`Asset <Asset>` object.
        :rtype: contentful.asset.Asset

        Usage:
            >>> nyancat_asset = client.asset('nyancat')
            <Asset id='nyancat' url='//images.contentful.com/cfex...'>
        """

        return self._get(
            self.environment_url(
                '/assets/{0}'.format(asset_id)
            ),
            query
        )