docs: def _cancel_expired_pending_orders(self):
          """ expires pending orders """
          # use a copy to prevent errors
          pending = self.orders.pending.copy()
          for symbol in pending:
              orderId = pending[symbol]["orderId"]
              expiration = pending[symbol]["expires"]
  
              delta = expiration - datetime.now()
              delta = self._milliseconds_delta(delta)
  
              # cancel order if expired
              if delta < 0:
                  self.ibConn.cancelOrder(orderId)
                  if orderId in self.orders.pending_ttls:
                      if orderId in self.orders.pending_ttls:
                          del self.orders.pending_ttls[orderId]
                      if symbol in self.orders.pending:
                          if self.orders.pending[symbol]['orderId'] == orderId:
                              del self.orders.pending[symbol]