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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 _possible_issuers(self, cert):
 """ Returns a generator that will list all possible issuers for the cert :param cert: An asn1crypto.x509.Certificate object to find the issuer of """


        issuer_hashable = cert.issuer.hashable
        if issuer_hashable not in self._subject_map:
            return

        for issuer in self._subject_map[issuer_hashable]:
            # Info from the authority key identifier extension can be used to
            # eliminate possible options when multiple keys with the same
            # subject exist, such as during a transition, or with cross-signing.
            if cert.authority_key_identifier and issuer.key_identifier:
                if cert.authority_key_identifier != issuer.key_identifier:
                    continue
            elif cert.authority_issuer_serial:
                if cert.authority_issuer_serial != issuer.issuer_serial:
                    continue

            yield issuer