Quantopian管道：ValueError：使用序列设置数组元素

Question

class PD(CustomFactor):  
inputs = [morningstar.asset_classification.financial_health_grade]  
window_length = 1  
def compute(self, today, assets, out, financial_health_grade):  
    print(len(financial_health_grade))  
    out[:] = financial_health_grade[-1]  

当我将其添加到管道中时，它返回ValueError: setting an array element with a sequence.

我该如何解决？