def _signature_scheme_changed(self, name, old, new):
        if not new.startswith('hmac-'):
            raise TraitError("signature_scheme must start with 'hmac-', got %r" % new)
        hash_name = new.split('-', 1)[1]
        try:
            self.digest_mod = getattr(hashlib, hash_name)
        except __HOLE__:
            raise TraitError("hashlib has no such attribute: %s" % hash_name)
        self._new_auth()
dataset/ETHPy150Open jupyter/jupyter_client/jupyter_client/session.py/Session._signature_scheme_changed