Python读取csv文件如何计算某列为空的另一列的和

Question

怎样得出K列为空E列的和呢

import pandas as pd
import numpy as np
import xlwt

count = 0
workbook = xlwt.Workbook()
sheet = workbook.add_sheet("Sheet Name1")

df = pd.read_csv("D:RULER_LINE_ABSOLUTE_PAVEMENT_EGDE_-distinct.csv")
had = df[["feature_length"]]
shen = df[["report_length"]]

sheet.write(count, 0, int(df.iloc[2]["order_id"]))
sheet.write(count, 1, float(np.sum(shen)))
sheet.write(count, 2, float(np.sum(had)))

workbook.save( 'sum.xls')

我这里只会得出两列的总和，如何能得出图中框里的数据之和呢
因为要处理大量的类似文件，所以不能确定是几行几列，只能确定对应的是空