code: def close(self):
          
          if not self._connection or not self._parent:
              return
          if not self._parent._is_active:
              # pragma: no cover
              self._connection = None
              # self._parent = None
              return
          if self._parent is self:
              yield from self.rollback()
          else:
              self._is_active = False
          self._connection = None
          self._parent = None
docs: Close this transaction.
  
          If this transaction is the base transaction in a begin/commit
          nesting, the transaction will rollback().  Otherwise, the
          method returns.
  
          This is used to cancel a Transaction without affecting the scope of
          an enclosing transaction.