def get_leaf_certificates(certs):
    """
    Extracts the leaf certificates from a list of certificates. Leaf
    certificates are ones whose subject does not appear as issuer among the
    others.
    """
    issuers = [cert.issuer.get_attributes_for_oid(x509.NameOID.COMMON_NAME)
               for cert in certs]
    leafs = [cert for cert in certs
             if (cert.subject.get_attributes_for_oid(x509.NameOID.COMMON_NAME)
                 not in issuers)]
    return leafs
Extracts the leaf certificates from a list of certificates. Leaf
    certificates are ones whose subject does not appear as issuer among the
    others.