def type(self):
        """
        Return the type of the object we wrap.  Currently this can only be
        'RSA', 'DSA', or 'EC'.

        @rtype: L{str}
        @raises RuntimeError: If the object type is unknown.
        """
        if isinstance(
                self._keyObject, (rsa.RSAPublicKey, rsa.RSAPrivateKey)):
            return 'RSA'
        elif isinstance(
                self._keyObject, (dsa.DSAPublicKey, dsa.DSAPrivateKey)):
            return 'DSA'
        elif isinstance(
                self._keyObject, (ec.EllipticCurvePublicKey, ec.EllipticCurvePrivateKey)):
            return 'EC'
        else:
            raise RuntimeError(
                'unknown type of object: %r' % (self._keyObject,))

        Return the type of the object we wrap.  Currently this can only be
        'RSA', 'DSA', or 'EC'.

        @rtype: L{str}
        @raises RuntimeError: If the object type is unknown.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/ssh/keys.py