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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 match_owner(self, url):
 """ Finds the first entity, with keys in the key jar, with an identifier that matches the given URL. The match is a leading substring match. :param url: A URL :return: An issue entity ID that exists in the Key jar """

        for owner in self.issuer_keys.keys():
            if owner.startswith(url):
                return owner

        raise KeyError("No keys for '{}' in this keyjar".format(url))