怎么新增一个字段

date = '2018-03-29'
code = 'SZ000975'
x_op = data.loc[(data['secode']==code) & (data['mkdate']==date),]
x_op = x_op['_r_Fop_1'].tolist()
# vv = [float(i) for i in v ]
x_op = float(x_op[0]),type(float(x_op[0]))

data['juli']= data['_r_Fop_1']-x_op-2