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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 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])