多头有仓位，如果需要平仓（或者减仓）的话，对应的操作应该是多头平仓吧？为什么在vnpy中是空头平仓？

这个日常买卖语言和程序逻辑不搭配，没必要一定mapping 上，只要看看下面代码，注意Direction和Offset就可以
def buy(self, price: float, volume: float, stop: bool = False, lock: bool = False):
"""
Send buy order to open a long position.
"""
return self.send_order(Direction.LONG, Offset.OPEN, price, volume, stop, lock)

def sell(self, price: float, volume: float, stop: bool = False, lock: bool = False):
    """
    Send sell order to close a long position.
    """
    return self.send_order(Direction.SHORT, Offset.CLOSE, price, volume, stop, lock)

def short(self, price: float, volume: float, stop: bool = False, lock: bool = False):
    """
    Send short order to open as short position.
    """
    return self.send_order(Direction.SHORT, Offset.OPEN, price, volume, stop, lock)

def cover(self, price: float, volume: float, stop: bool = False, lock: bool = False):
    """
    Send cover order to close a short position.
    """
    return self.send_order(Direction.LONG, Offset.CLOSE, price, volume, stop, lock)