1.在Excel中定义新列：
#定义新列需要用到columns.tolist()函数,具体代码如下:
col_name=df.columns.tolist()
col_name.insert(新列位置, '新列名称')
wb=df.reindex(columns=col_name)
#然后后面再接一行代码用来定义新列的计算规则。
2.将结果输出Excel文件：
df.to_excel("path to save")
对一个文件夹下所有Excel批量添加一列，整体代码：
import sys
import os
import pandas as pd
from matplotlib import pyplot as plt
import math
import xlwt
import xlsxwriter
plt.rcParams['font.sans-serif']=['SimHei']#用来正常显示中文标签
plt.rcParams['axes.unicode_minus']=False#用来正常显示负号
path = r'file path'
filenames = os.listdir(path)
f = xlwt.Workbook(encoding='utf-8', style_compression=0) # 新建一个excel
sheet = f.add_sheet('sheet1') # 新建一个sheet
for i in filenames:
excel_path = r'file name/' + i
f = open(excel_path,'rb')
# print(f)
df = pd.read_excel(f)
#定义新列
col_name = df.columns.tolist()
col_name.insert(10,'1') #设置新增列的位置和名称
wb = df.reindex(columns = col_name)
df['1'] = df['2'] - df['3'] #计算方式，根据自己设定
#To save it back as Excel
df.to_excel("path to save/"+i) #Write DateFrame back as Excel file
参考资料：
https://stackoverflow.com/questions/44811523/how-do-i-add-a-column-to-an-existing-excel-file-using-python
Excel中新增一列 python：https://www.cnblogs.com/guxingy/p/12916940.html
