import pandas as pd
series1 = pd.Series([25,10,50],index=[0,1,2])
series2 = pd.Series([5,7,40],index=[0,1,3])
series3 = series2 + series2
#兩個序列不對等,形成缺失值。
series3_na = series1.add(series2)
#兩個序列不對等,形成缺失值將缺失值NaN預設將缺失值設定為0
series3_good = series1.add(series2, fill_value=0)