def asset_url_for(self, asset):
        """
        Lookup the hashed asset path of a file name unless it starts with
        something that resembles a web address, then take it as is.

        :param asset: A logical path to an asset
        :type asset: str
        :return: Asset path or None if not found
        """
        if '//' in asset:
            return asset

        if asset not in self.assets:
            return None

        return '{0}{1}'.format(self.assets_url, self.assets[asset])
Lookup the hashed asset path of a file name unless it starts with
        something that resembles a web address, then take it as is.

        :param asset: A logical path to an asset
        :type asset: str
        :return: Asset path or None if not found