主图绘制MA，第0根BAR左侧有MA，右侧没有绘制

while True:
    api.wait_update()
    if api.is_changing(klines.iloc[-1], "datetime"):
        ma = MA(klines, 20)
        klines["ma_MAIN"] = ma.ma  # 在主图中画一根默认颜色（红色）的 ma 指标线
        t1 = sum(klines.close.iloc[-20:]) / 20
        print("最新价", klines.close.iloc[-1], "MA", t1, "ma_MAIN", klines.ma_MAIN.iloc[-1])
        print("前次价", klines.close.iloc[-2], "MA", t2, "ma_MAIN", klines.ma_MAIN.iloc[-2])
        t2 = t1
        pass