Method _begin

lib/sqlalchemy/orm/session.py:1046–1055

(self, nested: bool = False)

        (SessionTransactionState.ACTIVE,), _StateChangeStates.NO_CHANGE
    )
    def _begin(self, nested: bool = False) -> SessionTransaction:
        return SessionTransaction(
            self.session,
            (
                SessionTransactionOrigin.BEGIN_NESTED
                if nested
                else SessionTransactionOrigin.SUBTRANSACTION
            ),
            self,
        )

    def _iterate_self_and_parents(
        self, upto: Optional[SessionTransaction] = None